I'd figuratively have a heart-attack great enough to tumble the mountains if Sega announced a new Shining Force for the GCN. Shining Force 1 and 2 for the Genesis are my favorite strat's ever, just ahead of Dragon Force for Saturn and Advance Wars. I'm super anxious to find out more about this VF Quest game--it's seemingly been in the works for twenty years.
That said, only two things I can think of could equal or top nearly anything Nintendo themselves could announce and those things are:
1) a 2.5-D (or straight-out 2-D) Sonic game eschewing the Adventure-style Sonic gameplay. My dream back in the 16-bit days was that when new systems came along, the companies would actually make games like the ones we had but with 16,000 colors and much more animation and CD-quality music. Sadly, this never really happened, with few exceptions. Everything just went 3-D (I know, I'm beating a dead horse that's been thrashed a thousand, thousand times already) and much of it just will never truly work. Nintendo proved it can be done equally or better, but Sega's Sonic games have done nothing but make Sonic fans wish for 2-D again (even though I think Sonic Adventure was a lot of fun).
2) One word, and it's so predictable: NiGHTS.
Let me add a third just for kicks:
3) Phantasy Star 5 (screw this online stuff for just a while).
(Oh, and I don't think this was solely a Sega game, but I'm dying for an update of the classic Wonder Boy in Monster World games!!!!!!! Isn't everyone? Hahaha...they could even use that Tenacious D song for the heck of it. Or not.)