I'd propose managed rewilding. (A bit of a contradiction in terms I know, but you can make it work). Whatever grows well (and seeds well), as well as what is in the soil will come up, and you'll get an interesting and educational succession of plants ending in a self-selected wood. There will be plenty of educational discussion to be had about weeds and invasive plants, natives and non-natives. Try to get a working group of local schools to do the decision-making, under the guidance of an ecologist, perhaps.