Of all the problems you listed, the fact that merchants don't use it seems to be the most important, and that can be addressed. Let's get more merchants using it!
And it's not just merchants but also...
Yes, totally agree with the peer to peer use case also. Amounts not so large that need full security of on chain (avoiding potentially high fees and confirmation times), but larger than small lightning amounts (amounts that may require more lightning channel liquidity management).