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"they could surely only withdraw licence for future versions"

Uh? Copyright law might be even more insane than I feared, then. If I give you money for a thing and then years later decide that I don't want the thing anymore, my right to say "I changed my mind, give me my money back." is, shall we say, severely limited. Likewise, if I give code to a large collaborative effort for some reputational benefit and then decide years later that I've changed my mind, then at best I would expect to have to return all those years of good reputation.

I'm not sure if that is actually possible, in which case they simply cannot revoke their permission, but perhaps all Linux desktops could display a list of offenders names and mugshots (instead of wallpaper) for a period equal to the age of their contribution at the time of its withdrawal, underneath a banner heading saying "These people are selfish scumbags.".