Deeper OS integration would be nice, but harder to roll out. I think the plan early on was to make something useful/generic/agnostic enough that a couple of big browsers would add support, then it could try becoming a Web standard.

Unfortunately that hasn't panned out; but it still feels more feasible than getting Microsoft and Apple to add it to their OS network stacks.

Pretty much impossible because of the incentive structures OSes have. Microsoft and Apple want to surveil you and Linux is a fragmented bazaar.