Is there a way to get the iteration number in a "block begin - block end" loop to control any parameter in the nodes inside the loop?
If there isn't one, then a question for the developers: are you planning to add such an obvious and necessary feature?

No; there is no easy way.

The hard way is to make something like a Constant Layer that you Add One to each iteration; and add to your set of feedback wires. But that is just a painful workaround for something that should be just an @cop_iteration expression in a parameter!

Yes; we are planning on adding such a thing. But I'd rather not promise anything that isn't shipped.