Another happy UAD V8 & Sonar Platinum user here. I did have to resort to the compatibility mode when I first installed the UAD plug-ins on my new DAW late last year, but thus far the updates have installed without a hitch.
I no longer install the x86 versions because I don't need them, so I can't comment on conflicts with them, but when I was installing both I don't remember having problems.
As far as UA moving towards Mac centric - I'm not sure I agree. There are issues with Windows and Thunderbolt, and UA have clearly chosen Thunderbolt as their interface of choice. It is a very sensible solution if you take the long view, it extends the PCIe bus outside the chassis, and that is a very cool idea.
In the short term it means that Windows users get the short end of the stick, which is unfortunate. If I were running the company I'm not sure which path I'd have chosen, even though I am a Windows user. The new versions of Apollo suggest, to me at least, that they have not forgotten us.
Now whether or not they should have pointed the fickle finger of blame towards Redmond is a debate I choose not to join<G>!