This is more of an "FYI" than arguing for it to be changed. American English almost always uses the singular form of a noun when it is being used as an adjective. Apparently British English has some rules for when such adjectives could/should be plural. (http://david-crystal.blogspot.com/2010/05/on-plural-adjectives.html)

The determiner "every" appears to be missing an object.

Also, while one can "organize" a meeting, it is not normal to say that one "participated" a meeting. I think "attended" would be the proper verb. I think it is because participate is reflexive.

Is this statement sufficient? Or do we need to have them actually sign the FPCA?

As mentioned before, "participated by" should be "attended by".

s/one needs not worry/one need not worry/

s/they would be the ones/they would be the one/

"They", in this case, is being used as a shorthand for "he or she". The pronoun is referring to a single individual.

s/add names to the agenda list/add names to the roster/

s/there points/their points/

s/arbitrator/arbiter/

s/try best to reach the middle ground by avoiding conflicts/try to reach middle ground and avoid conflicts/

s/get their opportunity/gets their opportunity/

s/be them/be they/

For https://pagure.io/fedora-websites/pull-request/1158#comment-172948, I think it would be best to leave it at the FAS account owners' discretion to have signed the FPCA as ensuring that feels a bit intrusive.

LGTM. 🙂