Hi Bill,
Looking at their price list for 2014 there are 5 conversions for the Riich carrier listed but Not Yet Available. I would think Resicast will wait and see what direction Riich take the carrier in before they commit to anything new as there is little point in doing a conversion in resin that then becomes available in plastic.
Still available though is the 10cwt trailer that was towed by the UC and their 10cwt trailer loads one of which is specific to the 3 inch mortar and recently they released 3 inch mortar wooden ammo boxes.
Resicast already have a selection of excellent UK wireless sets so for anything new carrier wise, it will probably be a case of if there a need that is sustainable to make the time, money and development effort worthwhile.
Unlike Tamiya, Riich are quite likely to produce further versions of the carrier so doing any AM kits might be pointless, and as both Riich kits are excellent kits and require no AM for a decent build, there is little scope there.
Those would be my thoughts, based on what I've read and seen regarding the Riich carrier.
Looking at the surge in product types becoming available from Plastic Manufacturers in British and Commonwealth kits, many of the bread winners for AM companies no longer exist, so they are more likely to look for new sustainable products than to keep flogging a dead horse.
Again those are just my thoughts.
Al