How does one come to the conclusion that the maturity of an 8 year old web framework, beats out the benefits of the almost 20 year old battle tested Java ecosystem. Not to mention the Scala Ecosystem is included as Icing on the JVM cake. OP also compared Lift to Django. How does OP not mention Play? Although an argument about the better of the two would be based strictly on opinion, from my view Play has more momentum in the race for the premier Scala Web Framework.
Coming to django, I would argue that it is the best documented project on this planet! Django has a huge number of plugins, quickens the process, and is based on some amazing philosophies(DRY) and you happen to admire what a big deal it is when you go deep into design of your web app.
Also, I can even argue that I can get a programmer who doesn't know python to start on Django in 4 hours. Now, I wouldn't bank on this point as it is a language ecosystem point, but it is a true fact, happened to me some years ago.
Lift, is cherry picking features from django/rails, which is actually a good thing, but I see it being a lot less progressive as compared to Django even at the scale at which Django is right now.
Play, I haven't used, so cannot argue much on that. I think Play2 is less than a year old? Surely, I cannot let my startup developers write more bytes than necessary. Why code something which is already done and that is precisely what happened with us when we started working with Django. Well tested libraries can be pip installed.
I'm a long time django user. I love django. I've used it in production apps. I like to try out new languages as a hobby and so I got myself the programming in scala and the Play framework in action (manning). Just trying out Play however I can't seem to get this feeling that I could do it more easily and faster in django, though that may be because I'm comfortable with django and python. There are also a ton of django apps that I can leverage to build out parts of my app. I'm not sure about the play ecosystem in that respect.
I'm also specifically looking for advantages that the language itself can bring but since I haven't gotten very far I haven't discovered any yet but I'm hopeful that I will be pleasantly surprised.
Having said all that I just saw some play love coming from LinkedIn: http://engineering.linkedin.com/play/play-framework-linkedin
You can build cool stuff in scala + e.g. wicket, I've done it, but there's an extra layer of awkwardness to deal with that doesn't exist with python/django.
