Sorry but I see combat logging (by disconnection) and legitimate logging out in combat such a minor issue that it's simply not worth the effort to do much about beyond the 15s timer (which is quite adequate in my opinion) for menu exit and bans for combat loggers....
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It doesn't affect anyone in solo. I would argue its impact in a private group is minimal as those in such a group should be amongst friends who will apply their own rules about such things. So it's only a consideration in Open - so only impacts that subset of the playerbase for a start. Of those in Open only, in turn only a subset of those are affected as combat logging or exiting via the menu is arguably only a concern in a PvP engagement (a minority of the playerbase to begin with I would argue). And of those who regularly engage in (or get drawn into involuntarily) PvP, only a subset of those will even entertain combat logging or exiting via the menu as an option (and they'll be the attacked rather than the attacker?). My point being that, in the grand scheme of things, across the activity of the WHOLE playerbase and once you eliminate those circumstances in which it is irrelevant, I sense that those who combat log or exit via the menu during combat (and PvP combat specifically) are such a small minority that it seems not worth the effort to do much more about it (beyond the timer for exiting, and bans for combat loggers). Granted, it makes piracy more difficult as a career choice, but arguably only if a pirate mistakenly focuses on pirating players only, which is never going to work as they might like given the matchmaking, instancing, dispersed playerbase etc. And arguably someone who insists on combat logging or exiting via the menu in combat shouldn't be in open to begin with, mind you.
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So that leaves the psychopathic killers (again a small minority) who want to simply destroy other CMDRs for jollies and no legitimate in-game reason. In which case I don't actually care whether their gameplay is adversely affected by either combat logging or exiting via the menu in combat as it's what they deserve.