If the text is done and you're just waiting on artistic types to make beautiful illustrations, why not put out a work in progress PDF? Lots of far bigger RPG publishers do this, sometimes through DTRPG which helps wonderfully with updates. You also can get the benefit of many eyes helping (for free) to find and fix inconsistencies and nonsense typos. BTW — an update a month makes your backers feel better, even if there's not a lot to tell. Folks get twitchy when you leave them in the dark.