So ... has anyone else been using the Lacinia alpha's yet?
Yes.
There's been new api's added, and some refactoring deep in the code, but outside of some changes for spec compliance (concerning nulls in non-nullable fields) I think everything is compatible.
I’ve been seeing the doc sets being updated in Dash but I haven’t had a chance to try out or even see what’s changed. Is the change log a good place to get an overview?