The outcome will be very different from what u may expect. A unified platform would only mean that u get fewer games all round. You will no longer see Mario for the handheld and a separate Mario for the console. There will just be one game that runs on both the console and the handheld.
Probably there will be a minor decrease in the number of games produced, but Nintendo won't let productive capital they've invested in go to waste (developers, buildings, etc.) Obviously for that reason the output would be similar. What we'd probably see is a more diverse library though, since releasing a Mario platformer yearly won't fly. Having said that, we might find that most of Nintendo games won't take advantage of the higher-end hardware as much as they have in the past (see: Super Smash Bros.) Honestly, since I'm a multiplatform (PC/Nintendo) gamer I'd prefer a console where you have 20 Nintendo games rather than a console with 10 Nintendo games and 10 multiplat third party games. Nintendo should forget third party and work on buying as many developers/exclusives as possible, allowing them to produce enough exclusive games to interest consumers. They have a good, stable market as a second (or for Nintendo fans first) platform. People are just multiplatform gamers these days, and Nintendo would do well to find their own niche rather than trying to steal markets from Sony/Microsoft. If they make their systems different enough there will always be a market for their platforms and games.