I've had the same idea. I'm just starting out, and want to try out different yeasts, different ways to hop at 5min, flameout, secondary or no secondary, dry hopping or not...and it seems to me that the best way to test any individual change is to do a sort of controlled experiment by splitting one boil into 4 or 5 different fermenting batches, and trying different things with each one. That way you know the different tastes and characteristics are because of the different 'treatments' you split that one boil into.