Yeah Vray has been testing beta for Maya for AGES, but christ knows when it will happen.
As with software, render engines have their pros and cons as well. At the end of the day its down to the same thing - the skill of the user, its what you do with it.
Ive said this so many times in the past, Ive seen some real bad renders done with Mental Ray by people who want the latest gimmick for all its worth, and in a nutshell they havent a clue about the first thing on lighting with a basic 3 light set up=key, fill and back lights.
So mirek, you lost work because you cant use vray or max so use maya, with MR or basic lights. Architecture models have a distinct look about them, somewhere between photographic and studio (does that make sense) Im sure thats easy enough to reproduce
Personally I'd go with renderman these days though, it pretty much does everything - easier
As for a merger of software, I wouldnt worry, if it happens we cant stop it, and if so I dont think it will for a while yet, I feel they've just turned a corner with the 2008 releases of Maya and Max. Maya is incorporating Mudbox most likely in the next release and yet mudbox will still sell as a stand alone package too so its 6 of one and half a dozen of the other right now...