I'm sorry, but that's untenable promise and I think that's exactly what he's asking. he wants to ensure that he can do whatever he wants, and while I believe he should have his stake, he needs to make promises to the community that he won't use it in certain ways, namely to take almost total control.
The top witnesses may be able to "promise", but like you said, that doesn't mean the rest of the community will allow it. I would for one remove my vote if the power down was reduced too much. The exchanges deserve the bed they've made and reducing the power down time too much puts the entire network at risk. That's the witnesses point when they say they can't really promise that now or ever. They can promise to try. That's really it.
I would also remove my vote if they took away the free downvotes. I was wrong to oppose them in the beginning, and have seen their use better the network overall so far.
My larger point here is that Justin is making the demands, when it should be the other way around. I've done some investigating on Tron and it's filled with junk apps overall. Nothing but gambling apps and Sun controls something like %40 of the network. There's no reason to really believe it would be any different here. With Sun being able to move exchange stake in and out rapidly, I have a feeling the same kind of apps would spring up on Steem and ruin it.
EDIT: Also, I believe that the witnesses have said they would unfreeze it so long as they could come to an agreement about what he would do with it, which he refuses to do. So...
RE: Meeting between Justin Sun, Korean Stakeholders, Steem Witnesses and Steem Foundation 12/03/2020