Uh, several more years?
Yes, years. Libratus uses 16 Terabytes of memory for just a 2 player game. The size of the game tree increases by at least a factor of 1000 when moving up to just 3 players. That's significantly more memory. Also the computations themselves take much longer when there's more than 2 players as something called "card removal" comes into effect.
I have a theory that it's impossible to prove anything, but I can't prove it.