Oh hell yes this has been bugging me for ages as well. As a staunch 2D Football Manager player being able to incorporate custom pictures in the background (a.k.a Stadium Pictures) would be such a bonus.
Unfortunately I fear 2D is nothing more than an afterthought to SI nowadays. Such a shame as I find the 3D completely unplayable. The graphics and animations are so poor and repetitive it very much takes me out of the game. 2D leaves so much to the imagination that the game as a result feels more realistic.