I can understand that point of view but I like and use both. The Plex media manager is really a step forward and integrating it into an unRaid server would be a match made in heaven.
On the other hand they need to improve on the player side, since Mac minis are expensive. If they can get the Apple TV player up to snuff it will be a step and we have to see what the LG rollout brings.
There has been some hints of some "powered by XBMC" hardware hinted at on the XBMC forum so maybe CES will bring us some announcements there. Now that Dharma is finally out there should be improvements of the XBMC side as well.
I'll probably keep both since I love playing with them.