Yes, I'd like something like that too, I'm in the same boat. My nas is not really beefy, but there is always at least one other computer running in my network that could be used for stuff like that.
Jenkins CI does something like that for running compile jobs. Very handy. You just assign one or more 'worker nodes', and it farms out cpu- intensive tasks to those.
I had the same idea as well. I have a Synology DS412+ which can do the job but if you want to stream several movies at the same time it is laggy! I have a simple HTPC with a AMD X1 fusion and it is waaaaaay faster to transcode so it would be nice to use it to transcode as it is almost always on as well.