> The game is still very popular and easy to play. But the obsoletness of DOS

Nothing obsolete about DOS when it comes to playing 2D games. Thanks to DOSBox and other emulators (FreeDOS is also not bad though) it is a fantastic OS (or virtual machine). DOS as a platform for (2D) games has never been better than it is today, on modern hardware running DOSBox.

This assumes that we can get a locked down, secure, stable bedrock system and sandbox that basically never changes except for tiny security updates that can be carefully inspected by many independent parties.

Which sounds great, but the way things work now tend to be the exact opposite of that, so there will be no trustable platform to run the untrusted code in. If the sandbox, or the operating system the sandbox runs in, will get breaking changes and force everyone to always be on a recent release (or worse, track main branch) then that will still be a huge supply chain risk in itself.