As "unstable" changes and "latest" becomes no more, these sorts of links should be updated to reference the approximate section they intended to reference at the time of writing.
This change tries to link up the relevant bits for the time of the proposal, though it's not a perfect match. Some MSCs were brought into the spec before an API version could be assigned to the "old" text, so github permalinks are used instead.
Note that MSC1831 changes the order, so the changes to MSC1708 might not make sense when combining all the proposals together. However, independently the change should make sense.
The main reason for this is that Apache etc won't stick a content-type on by
default, because they don't know it's JSON, so requiring it seems like it will
require unnecessary hoop-humping for everyone who wants to use a .well-known.