Like their source material is right in their laps, Eiichiro Oda did the leg work for them! Sure they have to stretch it a bit more to fit a length of a special but that's easy and sure you have to rearrange some characters. Like I think Roshi would be paired with Brook now, both being old as dirt perv's. Hell have Troiyama just come up with some idea or hell Oda again, he's a workhorse, unlike Toriyama but I'm sure you can get some ideas out of him.
Plenty of Dragon Ball main cast and One Piece cast have done some work on each other shows.
They are all under umbrellas of each other companies. Jump owns both manga, both are animated by Toei, both are under Fuji TV and both have merch/games made by the same company Bandai.
The only thing stopping it I think is that, both shows have different producers, at either Toei or most likely I think Fuji TV. This could be the explanation for why the Toriko X Dragon Ball X One Piece hasn't seen any rebroadcast, streaming release, physical release or dub....because old ass producers don't want it for what ever reason.
Outside of small promotional stuff seems like a shame to never make an official animated cross over like the manga audiences got, which seems like a waste.
Here's some of those cross promotions:
Too close here's the ugliest looking Luffy drawn by Toriyama
