hello, will it be available soon S4mk4?
Probably not soon, if ever.
What is soon for you?
Looking at the 'speed' of Traktor development and what's going on a NI in general I wouldn't expect one soon and I feel the current controller is still very complete and attractive. You could consider getting a used one.
More important now is that the software is being taken care of and with what is on the roadmap so far I'd say the controller is still fine.
S4-MK3 is great, but we expect innovations (display, stems in real time)