The learning curve will mostly be dependent on your general typing proficiency.
I was at 120wpm on the vanilla keyboard before I got the Ergodox.
For the first few days i was topping out at 110wpm, because i decided to switch a bunch of letter placements for better orientation on the column layout.
After 2 weeks I was back at 120..
I would say, if you're at 100+, there's very little transition work..
If you're at 60 to 90, it will feel a bit more strange..
-- Typing mastery is more than just layout, it's also adaptability, users at 100+ are more adept at typing, but also at assimilation of new motions. This is because when you do something repetitive, your brain automatically dedicates more brain area for processing of that task.
And after a year or so, I've reached my current top average speed 135wpm, 145wpm Lucky words speed.
I have not gotten faster after that year.. haven't spent much time trying, but i don't know if i have the potential..