Say I have a type of machine, and I want each tier of machine to have it's own structure type (allowing me to limit input/output rates and structure design)
Right now I would have to add a recipe for each machine tier, and that's wasted space.
This could also be used to limit recipes to a minimum tier (example: glowstone can only be centrifuged in a tier 2 machine or higher)

So? Machine-Controller tiers and then have an option to make recipes require >= a specific tier?

More like having a different multiblock setup per tier, not the controller.

So, this would mean having machines registered under the same "registryname", but different "tier" so that different multiblock setups can be defined

And yes, having recipes require an optional >= for a tier would be nice too

That works too. Didn't think of it like that, but that would be easier to implement for the users and you.
Just adding the ability to add recipes to multiple machines is fine with me

So rather making recipes assignable to more than 1 machine?

That is rather easy to write yea. Adding it next version.

http://i.imgur.com/rzufC8l.png Added next version.

Added as explained in v1.3