If it's not legal tender, they can't regulate businesses accepting it via KYC-only. It would be like things currently are, where business would have to convert anything they took to fiat for tax reporting purposes. They could still ban it outright, but that in and of itself is easy enough to get around.

Yeah, selfhosted lightning isn't something Joe Average is ready for, but I'm assuming that things will get easier on that front in the next few years (possibly a bad assumption).