Has Unity ever said anything about turning their software into a platform, for instance asking for monthly/yearly subscriptions instead of a one time fee ?
If they did, that's when the devs (and especially teachers of future devs !) should have dropped it as soon as feasible.
platform isn't just about subscriptions, subscriptions don't really make a platform, and overall it'd be kind of a poor tell of whether it's time to jump ship. epic/unreal is kind of a platform (there's a bunch of stuff in their ecosystem that plugs in, etc.), so what, should people jump ship from unreal now
You're right, it's not a sufficient condition (pretty sure Red Hat offers Linux support in subscription form), you also need to have closed source software for a platform.
I don't know about the situation with Unreal, but I would be very wary of using it, considering Epic has been pushing a game Store. (And Unreal's source code is merely source available ?)
Has Unity ever said anything about turning their software into a platform, for instance asking for monthly/yearly subscriptions instead of a one time fee ?
If they did, that's when the devs (and especially teachers of future devs !) should have dropped it as soon as feasible.