Idea: combat damage doesn't happen until endstep. The damage should still be tripled. Does this work?

Seems like a thing you could do. Though also - apart from flavour - why? Both it and the things hitting it still deal damage in the same step; it's just after main2.

"Prevent ... until" would need to be defined in the rules. Whether this works or not depends on whether you are able to write tight rules for this. As written and without change to the rules it does not work as the current assumption is that "prevent" means "replace with nothing".

You want to replace it with a delayed event rather than "nothing" - but in no way the rules recognize since they know e. g. delayed triggers, but those use the stack and your phrasing doesn't use any of the language associated with triggered abilities.