Excel functions are translated. This leads to being pretty much locked out of any support beyond documentation if your system language isn’t English.

The dev stated that it mostly exists for more performance-limited applications like mobile.

Expanse does too, though it isn’t common in that world.

Exactly. If you implement DRM that will make the software unusable if it can’t phone home, you should be legally required to have a plan in place for when your servers shut down.

MMO servers get a bit more complicated since they often rely on third-party components that aren’t releasable.

Only if the publisher has taken steps to stop individuals from preserving them through more traditional means.