I don't know if this is the case, but Android should have a set of guidelines specifying the current known hardware variations to test against in terms of screen size, memory and processing power. That devices take into account physical and on-screen keyboard should be a give, however.

The most likely thing is that different manufacturers will have some sort of certification process a la Appstore, but less restrictive in terms of allowed functonality. I know for a fact that Sony and Motorola are pointing that way.

I'm still pretty sure that within a year this situation will be normalized as more specific guidelines come up. Indeed, some devices will be left out. However as long as most devices have access to the important applications I don't think anyone will be too worried.