I don't think it's a good idea. Shutterstock is moving along fine. This would be too much of a drastic change and could destroy something that works really well for a lot of people. It would put too much favoritism on some contributors over others.
I like the new licenses, but you can still get ANY photo at the base price, depending on your usage. It's easier for the buyers and it's easier for the contributors. Keep keeping it simple.
Besides, if you're a contributor and this is what you want, you have choices already. You can work with iStock or go with the RM agencies. Let's not make all the sites the same. That would mean fewer choices in the end.