This is different. All nodes validate rewards, but current nodes do not validate the size of the coinbase script (according to the witness idea at least) and the script can be pretty much anything.

Creating new coins however would be a hardfork, no full node would accept it.

Also the "segregated witness" AKA. the "lets overcomplicate things because we are bankers"-non-solution is stupid.
All it does is destroy completely the beauty of Bitcoin and increases the block size limit to 4 mb ... so just raise the damn limit if that is what we want, don't do this crap.

Luckily there is zero chance of miners backing the witness proposal - many of the miners are even scared to give themselves the power to vote on blocksize! (BIP100)

Miners are conservative and respect Bitcoin because if Bitcoin fails they stand to loose their entire business.