does anybody know when poloniex will enable this?
It's not surprising at all. Bech32 format was only implemented very recently; it should be expected that there will be a significant period of time where the ecosystem is in transition. For all I know they haven't even implemented Segwit yet on their end.
You can always use a P2SH nested Segwit address to receive withdrawals from them in the meantime. It would be nice to have a hybrid wallet with both standard and Bech32 addresses for situations like this. This is the main reason why I haven't upgraded to a Segwit wallet. Not many people/businesses are interacting with Bech32 addresses at this point.