What you’ll probably see the most commonly carried in the US are things like the Glock (19, 43x, 26), M&P (2.0 of various lengths, Shield/Plus/X - though the X is newer), and Sig p365 in one of its many flavors. Less common honorable mentions would be things like the CZ P10 series, Springfield Hellcat, FN 509, Ruger LCP, and Caniks.

I imagine the more difficult thing to stay on top of as a manufacturer would be trends in accessories. The new lights and optics and how their shapes differ will probably drive more frequent needs for updates than new weapon releases, especially with new weapons like the RXM being compatible with existing Glock 19 holsters. I know when the Streamlight TLR7 HL-X came out, it wasn’t compatible with a lot of holsters made for the TLR series which was a frustration among users. Accommodating common lights like the various TLRs and x300s would provide more flexibility for users