I think it'd be good to release them under a timebomb license: closed source for 5 years, let the dev make money, after which they have to release their source under a permissive license.

Similar way is how I ended up finding out about Mindustry. Found it on F-Droid and liked it enough to buy it on Steam when I found out it's available there. Definitely a good idea if done right.

They could potentially release source only with no art assets. Then you wouldn’t be able to compile the game without either owning the game or pirating the assets elsewhere. But it would allow community members to update the game when it breaks or to add new features. Similar to the Mario 64 decompile.

While all this would be great for consumers it would probably take legislation to get publishers on board with something like this. Publishers have a financial incentive to let the games languish then force you to pay to get a “remastered” version.

I have purchased every single open source game that I've seen listed on steam as paid. Examples:

• Shattered pixel dungeon (and also the original Pixel Dungeon)
• TOME
• Shapez
• Open Hexagon
• Mindustry
• Lugaru
• Mega Glest
• Marvellous Inc
• Hydra Slayer
• HyperRogue

For more FOSS games on steam, there's a decent list collected on this curator (also pointing which ones are only partially open): https://store.steampowered.com/curator/38475471-Libre-Open-Source-Games/?appid=1769170

Part of the spirit of open source is that commercial distribution be allowed. So there's no issue with doing this.