Can somebody say when approximately may be released 1.8 RC1 ?
Mainly interesting "not earlier than ..."
Not anytime soon. It was not planned or discussed yet. There is some interesting development that must stabilize first.
I would say "not earlier than summer 2017".
On the other hand there will hopefully be many dot releases for 1.6 before that (1.6.4, 1.6.6 ... ?).