New design handguns often use non hi-cap style mags, forever making them only 10 round capable. Some of the smarter designers are using slightly modified designs that accept other model or make hi cap mags with little to no modification. One that immediately comes to mind is the new polymer Springfield.
I can not see how a manufacturer with a currently manufactured pistol that had preban mags available for it would modify it to take only 10 round mags for several reasons.
1. It would cut out the market for LEO and Military contracts.
2. It would make ALL old mags pre and post ban unusable, only taking to new 10 rounders they had.
3. Along the lines on #1, if they wanted to do this AND keep the LEO market , then they would have to have 2 production lines or re-tool every so often to produce the other model. Both of those cost money. Plus, everyone would just buy the hi-cap capable ones because they would not be illegal, just restricted by the manufacturer. A trick that often doesn't work, creating a gray market.
HTH!