Good question!
It's not actually possible to "plan" a GOG release as such, because their curators manually approve/reject every single game on the site. We submitted it for review months ago and it was rejected with no tangible reason given.
There is a glimmer of hope, however. You can vote on the Lucy Dreaming GOG wishlist here: https://www.gog.com/wishlist/games/lucy_dreaming :)