Anyone have an idea of pistols that are currently being equipped with Trijicon RMR ?   I see countless photos of M&Ps or Glocks but very little else

The only factory options are Smith & Wesson with the M&P CORE and FN with the FNX-45 Tactical. Everything else you see (Glock, M&P, XD, etc)  is custom milled....I've seen H&K USPs and PPQs custom equipped as well. The sky is the limit. Mark Housel is the man responsible for many great things, including the RMR equipped PPQ.

However Unity Tactical also offers their ATOM slide for Gen 3 Glock frames.....so that's sorta a "factory option".

Shameless pic of my Unity Tactical Glock 19 and FNX-45 Tactical -

I have the core and the fnx with rmrs

L&M will also install an RMR on a XD/XDM.

Check out Springer Precision, they have a mount for a rds that fits into the rear sight location for the XDM 5.25. I do not remember what red dots the mount is compatible with.