Me too – I'd much rather trust my password manager, so I'm hoping that platform/browser APIs will eventually become available that will allow such third-party implementations. (Android is planning to; iOS hasn't stated anything yet.)
Even then I would probably not add my bank credentials or other high-sensitivity things there.
That's a showstopper for me, personally. Not saying the idea is a bad one (at all!), but I won't be using it for myself.