I think that, unless there are questions that NEED to be answered, you should ask him less "specific" questions, and more "general" questions, so he has a chance to ramble on about things, and we get a better feel for what's going on inside his head. However, as a "plan B", you need a healthy stock of specific questions (more than you think you could even ask), just in case he doesn't feel like rambling, and you need to squeeze SOMETHING out of him.
Here's my input, organized mostly chronologically, so that it's not "all over the place".
01: What was it like, making the first Megaman (Rockman) game on the NES (Famicom) back in the 1980's? How did it feel?
02: Did you ever see the American artwork from the first game? ^_^
03: You made six Megaman games for the NES. They were all gladly accepted by it's group of fans (even in America), but did you ever feel that you had made too many? That maybe you went too far? Or you should've left people wanting more?
03.5: Does any one of the first six games stand out in your mind? Something more memorable than the others?
04: It's well known that in the NES era, Nintendo liked to exert "control" over third parties. Censoring games. Demanding improvements. Did this ever affect you and the Megaman series, and how?
05: Nintendo also demanded a certain "loyalty" to prevent newcomers from getting a foothold, but they loosened that policy when the Sega Genesis (Sega Mega Drive) emerged, so a Megaman game appeared on the Genesis. What did you think of the "loyalty" factor, and of the Sega Genesis in general?
06: What did you think of Nintendo's other early competor (primarily in Japan), the hardware giant NEC, and their TurboGrafx-16 (PC Engine)?
07: The Megaman series seemed to be "reborn" on the SNES (Super Famicom), with the highly-improved Megaman X (Rockman X). What was it like to make such a game?
08: What did you think of the SNES, compared to all the systems that had come before it? What of the "Super FX chip"?
08.5: Did you have any hopes for the ill-fated "SNES CD" drive? Did you ever hold off on making CD-based games for the other systems because you were waiting for Nintendo's version?
09: There were three MMX games on the SNES, along with an upgraded return of the original Megaman, with Megaman 7, and Megaman and Bass (Rockman and Forte). Did splitting the series in two help with trying to keep a "freshness" in the series?
10: For the PlayStation, MM8 and MMX4 didn't seem to show as "dramatic" of an improvement as the NES-to-SNES leap. Was there pressure to show some sort of reason for the technology increase? (The animated storylines were nice, but I thought Megaman's voice seemed out of place.)
11: In recent times, it's become more clear that Sony has their own ways of demanding "control" over third parties, wanting cutting-edge games, and discouraging the use of 2D. Did this hurt the natural "fit" of the 2D Megaman series on the PlayStation, when compared to something like the N64?
12: It was said that Sony asked that the "history" of the Megaman series be downplayed (perhaps in contempt of it's primarily Nintendo-based history), leaving some parts of Megaman 8 censored out, making the Sega Saturn version superior. Yet Sony also asked that their version be declared "superior", so it was called a special "anniversary edition", which contradicted the "history" downplaying. What do you make of all this? Does anything need to be set straight?
13: What's your lasting impression of the Sega Saturn? Could more American success have helped Sega to weather the arrival of Sony?
14: Many fans suggest that Megaman games began a downward spiral on the PlayStation. Considering that 2D games were considered "obsolete" at the time, was there pressure to put damaging new levels of "innovation" into the series, rather that just doing what you do best, or was it more that you wanted to take the games in new directions?
14.5: The Megaman X series linked itself to the classic Megaman series in the PlayStation games. Was this always your intention? Will we ever know what happened to the classic Megaman, to turn him into the Megaman of the X series?
15: The Megaman Legends 3D games on the Playstation were reasonably well received, but didn't really seem like Megaman, and the "Tron Bonne" spinoff was apparently well-liked by fans of the Legends series. Might the Legends series continue with new Tron Bonne games?
16: Megaman Legends looked more suited to the N64 than the PlayStation. And was even ported to the N64. Setting the financial requirements of the N64 aside, as a game maker, did you ever wish you had more opportunities to explore the N64?
17: What did you think of the Sega Dreamcast? Were you surprised that Sega would cut their losses so soon into the investment of a new console? Did you see some of the amazing 2D shooters that were born on it, in it's short life?
18: What motivated the fundamental shift in the Megaman X series, in making Megaman X7 go 3D on the PS2? Why not another rebirth, to make a new 3D series?
19: The Megaman Battle Network (Rockman.EXE) anime and GameBoy games don't seem to share much with the classic 2D games, but share a similar style and character design. Do you like making new games, with familiar styles, or do you prefer a new style, like the Onimusha games?
20: Do you think about the ever-changing age of your fanbase? Like kids these days playing Battle Network, who've never played an NES game?
21: The Megaman Zero games on the GameBoy Advance revive the old 2D ways. Metroid is recently returning to 2D on the GameBoy Advance, Castlevania is big on the GameBoy, in a slightly newer fasion. What do you think of the role of the GameBoy series, as a haven for 2D gameplay? Do you think that the Nintendo DS can continue that tradition?
22: Through the ages, what games have been your best competition? Where are they now, and what do you think of what they've become?
23: Regardless of modern 3D demands, do you think you and Capcom are capable of making a 2D game on a modern system that exceeds long standing high-water marks like the MMX series, or Castlevania: Symphony of the Night?
24: Super Mario Bros 3's latest appearance on the GameBoy Advance contained a way for new levels to be imported by e-cards. Since the e-reader was decoded by hackers, it's become theorectically possible for fans of the game to make new levels for the game. Do you think longtime fans of the Megaman series could be capable of making new Megaman games that could be good enough to be worthy of your respect?
25: Piracy of your Megaman games? An insult, or a (perhaps improper) complement?
26: Some have said that they day is fast approaching when there will be "too many" good games, putting game makers out of their jobs, and that games must eventually be "rented" online instead of sold, if game makers are to keep making money, or that the "online multiplayer" aspect should be the main focus of the game, and be controlled by the game makers. What do you think of such things?
27: What do you make of the success of the PS2?
28: How about the GameCube and XBox?
29: What do you think of the upcoming systems? Particularly, the upcoming Playstation Portable, and Nintendo DS? What are the biggest "unknowns" of each?