An interesting idea, but it's not clear that this will be less confusing or that application authors will make better at avoiding config languages gotchas than config language designers such as yourself (and existing app specific config languages suggest otherwise).

I think a reason this won't necessarily fix the problem with unmet expectations is that identical constructs in different but analogous yaml files would be likely to end up with very different semantics and users effectively have to remember which particular idiosyncratic YAML dialect choices various apps make. Say

   version: 1.3

means the string "1.3" in app a), the float 1.3 in app b) and a version number in app c) one. Furthermore let's assume that app c) required a version number, whereas a) and b) required strings.

Another, more subtle problem, is that such a scheme would make it more likely that applications would end up parsing raw string representations themselves (with ensuing subtle differences even for things which are nominally meant to be identical, say dates or numbers and possibly security problems as well).