As a long time DF player you should know that it is never advisable to wait for next version. I am very new to this game, but I can certify that current version is playable.
It'll be called 6.0, and while it will have a number of improvements and changes it looks like gameplay will remain pretty much the same. If you're excited for Aurora, go ahead and try it out.
I don't think the interface will be much different, there will just be new windows and overview tools added.
We do not have an ETA, if I had to guess I would say probably within a month or two, but it all depends on how much time Steve has to put into the game, and exactly how big the changes are. It seems that the changes are fairly large so who knows.
Long time DF player here thinking about trying out Aurora, but I'm wondering if I should wait for 5. 7 to come out? I'd hate to have to re-learn the interface right away. I don't suppose we have a rough eta for its arrival?