John
I don't see a problem with Mac and PC people coexisting. As long as each has their own forum there should be no problem. One issue I have thought of is there will be no long time users to help Mac users with any problems they encounter. It may be an adventure for some and a huge headache for others.
I would hope the interface and operation of Sonar itself would be consistent, or as consistent as possible, between PC and Mac.
Assuming that to be the case, the most likely issues I can think of are to do with the very different directory structures, file-systems and naming conventions associated with them, in the sense of "what goes where" and OS X's Audio and MIDI studio configurator. Hopefully most issues to do with the OS will boil down to "install any necessary drivers, enable them in Sonar, that's it, you're done". Most of the PC issues around dpc latency, wi-fi clobbering audio latency, one driver conflicting with another etc. don't seem to happen in OS X.
It would be great if Sonar for Mac supported AU plugins as well as VST as well. That way people with lots of existing plugins won't have to start tracking down VST versions, and if Sonar for Mac takes off may help avoid lots of "where are my 1,243 existing plugins, why doesn't it see them" threads.
Personally I really hope Sonar does take off on the Mac. Having used Apple kit for non-DAW purposes for quite a while, my one and only PC (see sig), decided to start acting up badly and randomly about the time the announcement about Sonar was made. I already have Logic on an i7 MacBook Pro because of some stuff I was doing with commited Logic users, and having tried Win10 I really don't like it, so I decided not to update Sonar this year and wait and see what happens..................