Personally, I'll be switching to RMU, with designing in RMC & RMFRP as I write material for use with Rolemaster Rome.
I can easily see that peeps will be using the older iterations, as that is happening even now.
(One point of contention with my ex-partner and I was that, since I had the older iterations I could play with, there was no need to pick up RMU. My...
ex-partner.
)