Good coincidence, yesterday I switched to a split keyboard. I had been programming since 2011.

Main reason for my switch is that I felt that my shoulders have a wider stance than before. I don't know if it's because of an improvement in fitness (I do a lot of shoulder and back work), or maybe with age I lost a bit of shoulder internal rotation mobility.

Either way, the learning curve was like a few minutes for me. Guess it's a perk of experience and the habit of touch typing.