I have asked this question what is the difference between port-channel and etherchannel And it appear to be the same. isn't the tag combinaison a source of confusion ?
As Cown explained in his answer, there's a difference between the two terms, although they can be related.
I don't think changing all tags to one of these two would be a good idea. Using port-channel would not make sense for questions about platforms other than Cisco's (and very similar brands). Using etherchannel would mean that everyone searching ofr answers using the port-channel tag would not find their answers.
Therefor, I think it's best to keep both, and make sure that some relevant questions (like the one you linked) use both tags, so there's a fair chance of them being found regardless of which terms a visitor uses.