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Of the active nodes in existence few if any of them would be effected by this hardfork(most users don't even know that they need to contact their ISP and unblock port 8333 which is blocked by default by almost every ISP) so the fears of centralization are exaggerated. ...
Huh? None of the handful of consumer-land ISP's I've had since 2011 blocked incoming high ports by default. Sounds to me like you are confused about the difference between 'contacting your ISP' and 'logging in to your router'. Or you signed up for some kind of nanny-help-me add-on from your ISP.
Of course many ISPs block out outgoing 8333 by default . Why do you think we see all these threads where people complain that they are getting only 8 incoming connections on their bitcoin QT wallet? Why do we average less than 7k nodes worldwide at any given time?