For simplicity, the 338RUM will do everything the Lapua advertises to do.
A 338-300RUM or my 338 Mystic will beat them both.
My guess is the delays is because the Rem has to go through a full meal deal development not just a bit of machining. Wouldn't surprise me if the action dimensions are made bigger just to make sure it stays together.
I would suspect this action would do dual duty as a tactical as well as a dangerous game action. Don't expect it to be in the same SPS price range either.
At those types of prices, I would go look for a SAKO or spend some more and get a full meal deal custom action.
Jerry