I switched completely to Plex HT. However, I have tested PleXBMC and it works quite well. He even created an add-on that lets you control it via your Plex Android/iOS app. The major limitation is that a skin has to be modified if you want to full integrate your Plex library into XBMC. The skin he has modified himself (Quartz) is quite nice though. It will not conflict with your mysql library at all. In fact, in the Quartz skin it's super simple to switch between your normal XBMC library and Plexbmc.
The only other limitation I found is that not all the Plex channels work.