The problem is that this would add a tremendous cost to the BOM that wouldn't be justifiable. A lot of users want something that just works (this is the market for the Vero 4K) and don't want to be messing with RAM sticks.
A good desktop environment needs acceleration; memory wouldn't be the limiting factor here. The device has an encoder, but it's designed for real-time encoding in mind, so quality isn't the best.
The memory controller also caps out at 3GB.