It's a terrible idea to route all your traffic over tor. If you have any expectation of anonymity you'll be disappointed. Since tor does not do any application level filtering, it is easy for exit nodes to track you.
It's a neat idea but has the same problems as network wide tor routers.
This is kind of how i2p does it. Currently i2p has like 6 "reseed servers" which bootstrap you into finding some other peers. Once you are connected to the network you then can contact "floodfill" servers, which are essentially a distributed form of the directory authorities. Floodfills are autonomously chosen routers on the network, and distribute other nodes to whoever asks.
> Do current browsers entirely prevent a connection to untrusted certs when HSTS is set?
Yes. HSTS would not do much to prevent active MiTM. HSTS just tells the browser that it should only connect to the site over HTTPS. It does not mention which certificates are trusted.
It seems like you are hinting towards certificate pinning (https://en.wikipedia.org/wiki/Transport_Layer_Security#Certi...). Pinning would prevent rouge CA's from signing bad certificates, but pinning is hard to do on the web. It is mainly used with mobile applications from what I have seen.
If they wanted to make a memorable address, they would have to run something like Shallot [1]. This is essentially brute forcing private keys until you find the public key you want. Depending on the name, that could take a very long time.
Are you planning on making it modular? If you made it something similar to what DuckDuckGo (http://duckduckhack.com/) does that would be very interesting. I would also contribute if that was the case.