The firmware is based on OpenWRT, so wider device support will come. There are thousands of devices in OpenWRT's Table of Hardware.

I suspect having a lower variety of devices supported will help lessen the demand for assistance/support as any issues will become widely understood and easily resolved, when possible, and devs can do dev stuff, and not support and troubleshooting on a myriad of various device manufacturers and models.

As far as availability of this particular brand and set of models, yes -- importing from foreign vendors (e.g., through AliExpress) will be typical (albeit with additional expense). Once demand is recognized, local vendors then will import them wholesale.

TollGate is going to need further work before it is ready for wider use, so hopefully before then the project attracts people with further skills where it no longer is just a couple people having to do nearly all the dev work and documentation themselves.