It it's interesting and new, sure, but also seems super easy to abuse. There are many ways to get and buff Golden Ages without accumulating any GAPs at all. Wonders, Policies, Great Artists all grant instant ones and if properly buffed can last for a super long time. You can even get permanent Golden Ages in the later eras, fully negating any unhappiness in the late-game where unhappiness might pile up from Public Opinion or heavy War Weariness. Aside from that, getting GAPs from tile yields, policies, etc effectively become free happiness points that artificially lower the happiness threshold. I worry that this change would largely negate unhappiness penalties that should actually be pretty severe if not attended to by properly managing Needs.
Aside from all that, this new mechanic would now have to be balanced against the existing production, culture, gold, and other benefits (Mosques, Baths, I know there are numerous ones) of getting GAs, which would effectively mean nerfing these GA-centric strategies.
Hm? Being in a golden age wouldn't mean you can't suffer from unhappiness - the pool can increase/decrease during a GA.
G