Of course there will be discoveries but I think we have the basic core there.
And again, advances beyond Einstein are really more about how to make it or the facility, political will etc to make it happen.
I am inclined to think a big break through would be to discover what causes gravity. But I guess the the big real crunches are infinity or creating something from nothing.
I often think if we had some extra sense the answer might be obvious. Imagine if the population of the earth died out and aliens arrived and these aliens did not have the sense of sight. What a mystery windows would be. Imagine trying to work out why buildings, cars etc were purposely made with much weaker sections
I don't think we do have the basic core - we still don't know the origin of the universe. When or if we figure that out, THEN we will have the basic core. I have often said I don't necessarily think we will be able to figure it out - it may just beyond our tiny perspectives. But I DO think it is objectively possible to figure it out - I don't think the answer is that god or a superbeing did all the parts we can't explain.