Why don't we feed the plastics to the termites?
Many animals can eat through plastic to get to what they really want to eat. Among them: termites, mice and myself when battling against a candy wrapper. However, as far as I understand, none of them can degrade the plastic. You can do the test yourself and I'll guarantee the plastic wrapper will come out the other end of your digestive system. 

Nevertheless, several organisms have been identified to be able to actually eat and digest plastics, among them:


Bacteria: Like Ideonella sakaiensis discovered in japan.
Fungi: Like Aspergillus tubingensis discovered in the landfills of Pakistan, or Endophytic Fungi discovered in the Amazon, which seem to be edible, and there are some people offering small mushroom farms you can have at home to turn your polyester and polyurethane trash into food, they call it "FUNGI MUTARIUM".
Insects larvae: Like this plastic-eating waxworm.


That said, it could be possible that some species of termites eat and digest some kinds of plastic. But I don't know of any reports of it. In the comments, Jan Doggen pointed to a 2003 article of people working in that direction. But I guess given the lack of publications afterwards, it probably turned out that the termites were not digesting the plastics usefully. If you search the internet, you will find many references of termites chewing through plastics (like this one).