So there is another thread in similar vein here: https://www.sylestia.com/forums/?thread=108596 asking for a third type of board generally and offering suggestions. My suggestion is purely adding release boards to either Fall or Winter fest. (or conversely both, but I think just one would be a big boon + provide adequate benefit)

Both annual release events fall relatively close together in May and July generally leading to a situation where low value/spare project pets tend to pile up on the site for 10ish months out of the year and people who do a lot of breeding feel a good bit of opportunity cost releasing the rest of the year especially if they heavily breed one or two species. Adding release boards to one of these festivals would I think benefit the economy and players a fair amount and reduce the stress of leaderboards at a busy time of year as well as player stable organization but I don't think would impact the purchasing of additional stables intensely.