When will be version 2.7.x available as final-version?
Nobody knows. You can use nightly builds for now (they are pretty stable, unless you really need voice chat, then you should stick with 2.5.8 for now). http://www.igniterealtime.org/downloads/nightly_spark.jsp
This page only have nightly for Windows, where are the nighly for Linux?
You can try tar.gz (just an archive) version here Install4j
I have also found RPM versions, but i’m not sure how updated they are (judging by dates, should be the latest) x86_64