Would a "sorry this code is out of date" shutdown for nodes that fail to update in time be "a trainwreck" or just get such nodes out of the way so those that do upgrade in time can smoothly synch in whatever the new system turns out, by then, to be?
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-MarkM-
This depends on the time-frame. One a six month time-frame a major this could lead to serious problems. One a two year time-frame it would likely not be an issue at all. Was there not recently a time-out on a delayed change that had been implemented by Satoshi that made certain old clients obsolete.
The key here is that
delay could cause very serious problems because we will need to implement this with at least a 12 month delay or even better an 18 month delay or longer.