In your scenario, it is unclear why Ukraine is needed at all. If neither NATO nor Russia can use it, this country will simply be erased from the world map as unnecessary.
I don't think smaller countries are just the playthings of the great powers. I think they can have independent self-rule. But as to whether such an agreement would be agreed to, probably not, and probably because of your point. Both sides want to profit from Ukraine, neither side would allow Ukraine to be independent and neutral. But I'm not really serious in my proposal. I just wanted to make another peace proposal since it is the popular thing right now.