I am the project lead on BlackTie, my apologies for not responding to this message earlier. Unfortunately I have somehow stop receiving notification when someone adds a new discussion...
Onto your questions:
In the short term BlackTie is suitable as wholesale replacement for a Tuxedo deployment. Tuxedo and ourselves both implement the XATMI and TX apis and as such you should be able to relink your service and client code against the BlackTie libraries with no code change. If you are making use of Tuxedo specific APIs (FML/view/Jolt/WTC etc) then the story is a little more complicated. We do have APIs similar to Jolt and WTC so migrating code to these APIs should be relatively trivial, however we do not currently have an FML like API, although this is on our roadmap for 3.0 (perhaps a 2.1 release if it became something time critical. Also, BlackTie does indeed support XA.
BlackTie is a community project (rather than a product) so it is difficult to tell if someone has actually deployed it in production from my perspective, however I would not recommend deploying BlackTie until we release 2.0.0.GA. We are currently putting the finishing touches to CR1 (expect it sometime next week), after the community has had a play with it and assuming no issues we would look to rebadge it as GA the following week, so I would say it is safe to say that GA should be release end of August.
If you are interested in BlackTie, I would suggest downloading CR1 next week and taking a look at it and letting us know what you think.
Just to follow up on this, we have now released the .Final (GA) version which is suitable for replacing a Tuxedo deployment.