There is absolutely no "lock in" if you try out the beta.
Our sign-on process uses a modified form of SRP. (See the draft white paper). It is not a traditional "authentication" process and so can't use other SSOs.
It's more of a threat to us than you describe. If a potential team of N people have k members who need a Linux client, then that might cost us N customers, not just k.
In fact, probably the guy responsible for storing most passwords is your friendly sysadmin, and a lot of them won't get caught using a GUI on Mac or Windows ;)
There's a fair bit missing. For now, the web client is read-only but we have full intention to make it able to edit, it just wasn't something we had time to do before the public beta.
The app also includes filling directly into webpages (via a browser extension) so you don't need to copy and paste. This also includes the ability to save new logins as you create accounts. Filling Credit Card and Address information as well.
Those are the two big features I think. The editing will show up on the web side but the filling part won't since it relies heavily on the client applications to do a great deal of the grunt work.
We're well aware of the demand for a Linux client though. I think all of us on the team would love to see a Linux client, but "love to see" isn't enough to make it happen right now.
I have most certainly written about this in my report I hope to send up the chain today so your voices aren't going unheard.