i proved 13 years ago that a flat piece of plywood with foot straps was truly all i needed to kitesurf, no fins either. so why would anyone need a board in addition to the foil? why not just bolt the foil to a piece of plywood--functional?
same with me! got inspired by zero prestige back in the days! to be honest, a plywood platform with just enough room for your feet is all you need.
but there are some considerations. starting is a lot harder without a proper board, not impossible though. you need to do all you jibes and tacks in the air, very hard to do. sometimes when you get out of balance your nose will go down. in this situation a nice scoop catches the board and you are more likely to continue. no scoop and you go down for sure. in very light winds you start on the board and you sometimes need one or two kiteloops to get the board in the air. you need a board that can do that. last but not least, some foils don't float. if the board does not float enough the whole thing will sink.
but, on the other hand, all these features can be done with a very simple plywood board. two layers glued together to make a nice scoop, nice outline, four holes for the foil, some deckpad, wax or whatever and you are good to go.