I thought as a QA flag it's meant for where an end of a way is close to another way, so QA tools flag it as "maybe should be connected", but if it really shouldn't be connected because it doesn't connect in real life you use "noexit=yes" to say, "hey QA, no really you can't exit here it shouldn't be connected".

That's a bit different to "it does really connect in real life, but for various reasons we don't want or can't yet connect it, so I'll set noexit=yes so your QA tool stops flagging it". The latter would be best kept as an external list, similar to how StreetComplete "ignore" don't add a tag but instead maintain a private list of "ignored" quests.

In this case it likely does connect, so the QA is correctly flagging it as something that should be fixed.

People have different opinions of how much detail to map. If it's something that would be covered by a council development application, or something that might affect the development planning rules, I think it's reasonable to map. If it's covered by legislation, for example a heritage item on your property you can't destroy, or a protected tree you can't cut down, these should be reasonable to map. A trampoline that has no development/planning restrictions and isn't a fixed structure I don't see much point and mapping and think we probably shouldn't, but people still map them and consensus seems to be to allow it if visible from imagery.