Currently the draft manual does not address this issue. There has been some controversy about it. In the interest of having a written rule about it so the project can move forward, this proposed rule aims to simply codify the status quo given the lack of any consensus in favor of altering it.
It's sort of like the highways and people wanting a 'pure' thing of State/US/I- only. I feel that airside / Capitol Subway probably should be provided at some point, but as a 'bonus' style system, rather than a core thing. Other than the Capitol Subway, the access restrictions here seem less than the roads clinchable on military bases (though, tbf, we have tended to debate those and minimise to those where you'd have an reason for the guard at the gate beyond 'I want to clinch this road'). We also have bits of road mapped that you need a ferry ticket to drive.
As for stuff where you need ID to travel - I think the Spanish AVE trains have it (most don't cross the border, but even those that do never leave Schengen so wouldn't require passports for the actual travel - it's security theatre after the Madrid train bombings), so perhaps a bit of clarity there.
Also, when I went to the Zoo a month ago, was I not an authorised visitor - they let me in (after a bag search) onto their private land, and had the right to turn me away? Wasn't my valid zoo ticket an access condition to ride the train (at extra cost, so I didn't*) in the way a plane ticket is an access condition to ride airside people movers?
I have no problem with the status quo, but would like a bit crisper wording of what we're not/not yet including.
*A bit annoying as I can't make out from sources whether there's a second stop and thus something mappable. But not that annoying as all you get to see is some deer things a bit closer than if you were walking around.---
Looking back through the thread, the only outstanding issue where there might not be consensus that I can see is the 3 letter labels, but the implementation of longer ones wasn't seen as that useful by the person who implemented them on the systems they did so:
It's crap for metros and S Bahn services which mostly run through one city. My city district proposal really sucks.
I've (mostly) implemented it for HH S Bahn now but not for HH U Bahn (metro).
https://github.com/TravelMapping/RailwayData/pull/15/commits/efabe446010a5470e765f6ddb317785754e931c7
https://tmrail.teresco.org/hb/?u=michih&sys=deuhhs
It's different for long-distance services which usually have one stop per city / town only. I don't have such route in Germany though.