Is it planned to be able to dissociate the stemps live like the competitor serato?
Difficult to answer, since we don’t even know if it is planned at all.
And stems live separation must be implemented in the software, not in a hw controller
S4 as in new hardware? Or do you mean Traktor 4?
For software, see here: https://community.native-instruments.com/discussion/5305/traktor-pro-3-feature-roadmap
It's on the roadmap. No one knows when the version will come out.
From historical data we can extrapolate about 1 item from roadmap every 4'ish month. So maybe there will be a beta in 6'ish month?
But no one knows for sure.