Hey @jarvie sorry just caught your message, here is some answers hope it helps:

1. We are going to release signer apps for web, chrome extension, desktop app etc... these apps integrate a keychain and will work similarly than "Steem Keychain".
2. Our signer apps and SteemConnect SDK will use the "Steem URI" standard to talk to each other, if another signer app / keychain app is using the same standard it would be compatible with our SDK, this would make possible for an user to login and sign tx with a non-SteemConnect signer app.
3. It will not be necessary for the users to add an app account as posting authority.