TB would be ecstatic with just Gostisbehere for Drouin let alone the stack of great players your throwing at them. Also TB doesn't want any salary coming their way. They want young cheap players only or high draft picks or prospects. Couturier is too pricey for them and their needs. (Provided they can't resign Stamkos)
Drouin is still a prospect. The Flyers have Dmen prospects. Agree that both teams don't teams want to add money. Maybe a trade could be: Drouin for two of the following, Konecky, Hogg, Morin, Sainheim.