Those are all pretty cool ideas, I like the donation idea so they can keep their videos hosted and improve load time and performance! I think a concept like steem forever by @knircky could also work well within dTUbe since videos don't age as quickly as written content and users can find joy way after the reward period is over having the ablity to upvote it after that period would really come in handy and help cover your dTube monthly hosting
What can also work really well is a quick listicle option so perhaps you're watching videos on DIY you can add them to a list and then create a quick post to say DIY vids I like to share and link it to your video. Or link response videos and reaction videos on the same topic.
Since alot of dTubers like to create questions and responses its nice to be able to follow the trail, keep up with the conversation and encourage a natural trend happening on the site