@piper: sddm has improved in the last few month a lot - but is far from mature - to sum it up: if it works ok - it works ok - if not, bad luck. There are some corner cases i pointet out yesterday in irc, i see no movement in these bugs. Mostly these things are about language and keyboard settings, default values and missed functionality. All these things are in the bugtracker of sddm and need to be addressed - and the sddm team will address them sooner or later.
I agree that it is not mature enough and that at this point in development is no way ready to be default by siduction
However
(you knew that was coming) this is sid, for some of us, we like to try new things or to break things or perhaps both at the same time
For some that have a sense of adventure and know that your system can unfold to not booting, cause you to drink, smoke, swear more than normal, shit, sddm might be for you,