Discovery Island would be an expensive build - there isn't the sewage, electricity, water, etc. run to that island to support any more than what was there - a few hundred guests visiting a zoo type thing - and its been closed for almost 30 years so I suspect what infrastructure is there is in less than great shape (Discovery Island was a really cool place though, I went there once when it was opened).
On the other hand, if the Poly bungalows do well, I could see an very upscale
DVC bungalow community built on Discovery Island. Something like treehouse villas or Poly bungalows - individual stand alone units - not too many of them so you don't need a huge support infrastructure. High point requirements, private and out of the way. With Disney keeping some of them as cash units for VIP guests who need privacy.