Buy back is not the problem, the problem is exchange, waves token is lame to be on large exchanges, this is the fucking serious issue.
Mercury got listed on Bittrex in last months as Waves token. So it doesn't seem impossible.
There are far less Waves platform tokens on centralized exchanges than Ethereum platform tokens but like you said, it's not impossible. Tokes (TKS) is also a Waves platform token that was listed on Bittrex for a while now. There will be more Waves platform tokens listed on Bittrex and similar exchanges.