I kind of sympathize with this request, because if you do the soldier equipping only after the mission briefing (i.e. not already in the base), you may very well lose track which soldiers were in the first row or so and prepare accordingly (if you don't distinguish them in some other manner, for example by putting on a different armor). And you can't go back and redo this like Meridian suggested. But if there is no space to make this available, there is no space, end of story.
I suppose this mostly affects vanilla. Many mods have so many special soldier types which you usually sort out as going out first (e.g. in XCF rats and dogs) and you can use those to navigate which soldiers were the first ones to deploy.