I think it’s off the table primarily because if they ever actually wanted it to be on the table they’d have made an exception to it’s being de-canonized like they did for Darth Maul: Son of Dathomir.

They’re going to part it out (Rukh’s already dead in Rebels, isn’t he?) and use pieces of it as needed to augment whatever original stories they’re pursuing in the canon, but I don’t think Thrawn Trilogy is ever going to see an animated adaption.

Maybe when they reboot the entire series in 20 years, they’ll re-think it.