Here’s what I think they should do
Bring wash back. Make him alive again. If river can kill you with her brain (along with all the other stuff she can do) then bringing wash back is very doable. They keep cramming every new project (I mean it’s only books and comics but still) into the timeframe of the show and it’s just starting to feel too cramped (imo) bringing wash back would allow them to move forward while keeping him around which is what fans want. Maybe he could have some psychic ability for a while then have it taken away somehow. Idk. Or he gets brainwashed by the alliance and the serenity crew have to kidnap him and remind him who he is.