The 43X makes sense, they are probably listening to feedback from shooters who hate the short grip on the 43, but love everything else about it.
Got a 43 a while back for the 6 actual, to complement her G19. It's a great little gun, surprisingly accurate and controllable for being so small, but she hates shooting it with the flush-fit mag. The one with the extension makes all the difference in the world.
Got a PearceGrip +1 extension for the short mag, incidentally, runs great with it.
Sounds like the ten rnd 43X mags may not work in the 43. If so, lame.
The 48, as others have said, is something I've heard folks clamoring for for years. Surprised it took Glock so long to come out with it.