I think the answer to that question is that we don't know yet. If those new features are buried in the ROM, they'll go away unless PACman ROM incorporates them. If they're in a standalone file that can be flashed on top of the ROM, you'll be able to add them yourself. If they're an .apk, then you shouldn't lose them (unless you have to wipe the phone to install PACman).
One of the upsides to custom ROMs is that you frequently get new OS versions faster. One of the downsides is that you frequently don't get manufacturer provided enhancements as fast, or ever.