I'm not sure a home 'hub' is necessary, why can't HomeKit be a distributed service across all you devices? so your watch could still be a remote for the tv, or the lights, or the front door, or the toaster …
(Change your wifi network or password? Have fun updating a dozen devices. Get a new phone or watch? Have fun pairing to a dozen devices.)
Beyond that, from a security standpoint, I'd rather smart devices didn't all have direct IP access. There are enough security concerns with the Internet-of-Things. Mitigating large swaths of those concerns appeals to me.