finally rooted my tab yesterday and installed the MultiPlusWindows app.
All seems to be running fine, 2 apps or 4 apps on screen available, detached windows also available.
But no more app available in samsung bar, is there any way to add more multiwindowed apps with other method than described in OP ?
Actual phone : Nexus 5 16Go Red (old phone : Samsung Galaxy SIII)
Actual tablet : Samsung Galaxy Note 10.1 2014 Edition SM-P600 stock rooted with xposed modules (old tablet : Samsung Galaxy Tab P7510)