Seems like a good idea, though I do not know if a trinket pro would be fast enough. If you do run out of speed, a teensy 3.1 might also be an interesting (and about as cheap) solution. The problem with the inkshield you had is the reason why I added a relay to the board. If you press reset (not something uncommon), the printhead will rapidly and randomy fire for a few milliseconds, enough to fry half of the nozzles.
For all future printers, a printhead controller will be the most stable thing to do. It is indeed too easy to destroy a printhead, and I can only imagine how bad it will be if you have 500 nozzles instead of 12.
As for the 6602’s, I do not have a bulk address, I simply hand over the €12 a piece and buy them 6-8 at a time. I am almost completely through them, but for now I still have a few good ones. I wonder how many I will fry when I upgrade the Plan B controller to Due and start material experiments.