After Working on it alone for a year, the founder and original developer of Nova Launcher Kevin Barry has stopped working on Nova Launcher and the open sourcing efforts. More Info: https://teslacoilapps.com/nova/solong.html
Technically you can disable automatic updates for it. However at anytime the rights to Nova could be sold to anyone else, and not just a data miner some are talking about, and suddenly the app gets updated but possibly to the wrong direction given its massive install base.