I know that this isn't a direct solution to the problem (which is extra box space to store Fionavara's collection/spoils of war), but would an adoption system through the Playerdex help take care of some of these problems? Players would have the option to transfer unwanted Pokemon from their account into the Adoption Center, and other players would choose to take them in.
This would allow players like Fionavara to, rather than release Pokemon, give them a new home. New players would benefit the most from this, sure, but it could also be used as a way to distribute Event Pokemon. Have adopting a Pokemon cost a percentage wealth fee (to make it easier for new players and harder for wealthy players), and hand out event vouchers over the Playerdex to ensure that everyone gets their hands on one Event Pokemon.
