The thing is the Retro Design will not work with all franchises.
Mega Man is special. Look at the graphics, it is obviously dated, but the style is so great that it still feels fresh and special. Not every 8-bit game can have that feel.
I believe Mario still can, but I don't believe the same about Sonic.
It has to be truly, truly iconic characters that are special.
I dunno, I disagree.
I think the whole thing about the retro design that works is, at it's core, it's really not about the graphics. More so, it is about the overall package you are getting. Great gameplay, music and stage design. At the end of the day the core of the game is what matters and not so much the graphics.
Give us a good sonic game with the style of sonic 1 and 2 (or 3) and I think we could see similar results.
Now why is the "retro design" important? I think the main thing the retro design does is place limitations on the developers. In a good way. For example, the developers forcing themselves to use the mechanics of Mega Man 1 and 2 only made Mega Man 9 a more rich experience.
It brings the game and its design back to basics and I think that's why this could work for most 8 and 16 but franchises so long as it's done with the same care that Capcom has put into Mega Man 9. If every developer treats the game as if it's their next big game to be released on a system and not just a retro rehash we could see some truly great series revivals on our way.
I for one am crossing my fingers that this does happen