To me, 5e's backgrounds are simply an update to 2e's Kits, filling much the same purpose- you get a few proficiencies that make sense given what you were doing before you started adventuring full time, and there's a side benefit to along with it. It's worth noting that not all Kit benefits are universal- the Complete Fighter's Handbook specifies that the Peasant Hero only gains shelter and aid from members of his own community; similarly, the Noble Warrior gains benefits when dealing with nobles of his own culture and can only demand sanctuary in his own nations. OTOH, the Gladiator is recognized (as a Gladiator, at least) wherever they go, though this is presented as a hindrance, not a boon.
That 5e backgrounds don't acknowledge these restrictions seem to preclude the existence of globe or plane-trotting campaigns; there's an assumption that if someone plays a noble, the DM will make it work for their campaign, as if the campaign will take place in or near a particular part of the world forever.
And certainly, there are a lot of campaigns where this would work perfectly fine for quite awhile; after all, by default, player characters don't often become world or plane-travelers until higher level.*
*I know this isn't always the case, but I think it's fair to say it mostly is the case.
So what we're really missing is, as usual, guidance for high-level campaigns and any indication that background features are supposed to stop working at some point (or be replaced by something else).
I mean, for example, let's say I have a Folk Hero background and, after ten levels of adventuring, I manage to become a landed noble (say by liberating my Uncle's keep in the Kryptgarden, ala Dungeon #26).
Do the common folk still see me as one of their own? Shouldn't I have the same benefits as a noble?
There's no guidance here, and it's all left to the DM to decide. All indications are that it's assumed the DM will figure it out on their own, of course.
