It is the first time I see DI past refer to not absolute but relative past. I mean this action will take place in the (imagined) future.

No. Contrary to the common belief, the word ´kuşanmak´ may well mean ´wear´ , or rather, ´wrap a garment around the body´. If we tend to use it as ´take up against someone, or say , an army, then we can say ´ kılıç kuşanmak ´, which literally means ´ taking up the swords and the like against an enemy ´( The period when it used to be used was when they were mostly fighting with swords, probably )

Hope it helps.