Random Monsters Map Patcher – diverse neutral armies.

The main highlight is the variety of neutral units on old maps.

Are you referring to custom maps? But why? If the author created it that way, let it be; maybe they had a reason. If the author didn't include NCF support, that's also the author's problem: those who need it will add it. In my humble opinion, there's not much point in this; improving the quality of GSC maps is a different matter.

The drawback of RMG is that even though it places groups of creatures, they are not random in the sense that they don't change if you start playing the map again.

Why play the same random map multiple times? GSC is there so you can play different maps.
The file structure, by the way, is promising. Then it will be easy to implement connections, NCF, and everything else you want. And you won't have to wait 10 minutes at the start of the map for the script to process all the creatures ;)