How does platform's "Check for Updates" handle this? What happens if a user has an existing installation running on Java 8 (and
this is the user's one and only Java VM)? Does P2 tell the user that the new bundles to be installed require Java 11 but that the current installation does not supply this?
So far, p2 won't tell anything, and would install anyway, user would then click restart and would get an error in the log, most likely a NoClassDefFoundError with UnsupportedClassVersionError.
I acknowledge it's pretty ugly, but I wouldn't qualify it as a blocker as there are workarounds/solutions (install Java 11+) and no user data is lost (workspace and code can still be used against older versions of Java/Eclipse IDE). However, it's indeed something we need to anticipate, by trying to improve the story (with a fix on the bug, or with some strong documentation and communication, or whatever).