The RM Cyradon book will contain all of the setting info in the original Cyradon.
The rules portion has not been written yet, and the follow is the current plan -- which means that it is subject to change depending on how things go (and I dislike giving out info that might change)...
The actual RM rules will be mostly RMX. The skill list will be those in RMX, plus the ones (from RMC) that were introduced in the EAs, plus Diplomacy & Duping (will be in EA7). The current plan also includes using Maneuver in Armor as a single skill option. 40 DPs per levell, not stat based. (we might give humans an extra 5 to offset them not having not having any special abilities like Nightvision)
It is also planned that it will include Culture packages (also in EA7 - but Generic, where the Cyradon Culture packages would be specific -- the plan is that using a Culture package costs 20 DP and they can only be acquired during Adolescence (i.e. a first level character would 80 DPs, or 60 if a Culture is taken).
Included professions have not been finalized yet, but the plan is to have a generic Mage and Priest (i.e. you pick the order they are from and that changes certain skill costs (maybe) and determines spell lists -- the rules for this still have to be written.
Races - The available races will be those from Cyradon, not the standard RMC races. Cyradon elves only live 500 years (are NOT immortal), plus we need to have a viable lizardman (Nagazi), Gnome (Rhona), and Gryphon race (I already did up the Gryx in one EA), and that might mean changing them from their C&T versions -- we don't know yet.