I would suggest that a .rocks type domain would be redundant because the official .com or whatever is usually where all the positivity is. Often the owners of the .com try to manage negativity, and ensure their domain is a positive place, so another place is needed for free criticism. Im not sure many would trust a .rocks as independent.

Also, I can imagine something like an fabproduct.rocks would be a magnet for troll types and quickly descend in to a general bun fight arena.