Tried it: Yes! Radioddity FS-T3 actually works with RB18 driver. But it's not perfect. It's limited to 22 channels, while the real radio can handle up to 99 memory channels. 22 seems to be hard-coded in the RB18 driver. This is sort of a big deal because the radio offers no way to change squelch tones / codes without using a computer. Sometimes it's easier just to add another channel for a particular group or event.
Excellent, glad you looked to see if it was already similar to an existing radio before just starting a new one. Too many drivers are near copies of each other and I'm trying to crack down on that.
Also, the radio can do separate RX/TX freqs via its original software, making it GMRS repeater compatible. (Note that it is not marketed as GMRS. Based on signal reports, I suspect it forces narrowband for GMRS repeaters. Possibly because repeater inputs are in the same general freq range as FRS channels 8-14.) But the RB18 driver forces simplex.
Haven't tried other drivers yet, but at least 3 other files mention P3107. This is a good start though. As it is now, the RB18 driver gives the functionality one would need for pure FRS-only usage. I think we can do better for GMRS / PMR446 / 70cm ham / extra FRS channels, which the mfg's software already can do.
Sounds like you may be able to just subclass the existing driver and implement a different get_features() function which sort of defines the "rules" for the radio to add things like duplex or whatever. At least it'll be a start, and potentially just adding some functions to the base driver that your subclass can leverage even though the rules are tighter on the other models works well. There are also some examples of radios that have a "GMRS-only" variant of a ham/commercial radio you might look at for other inspiration.
--Dan