C23 is scheduled to promote bool, alignof & co. to keywords, so the concern for using _Xxx keywords is recognized by the committee. They introduce _Xxx keywords, sometimes alias them to lowercase versions with macros and let this age. Then, some time after, they switch to the "primary spelling", which is how the lowercase versions are referred to.

You can't easily lowercase _Type and _Var, so practically speaking it will take years before these features could be suitable for wide-spread adoption. Hence my original comment - given the friction, is it worth expanding the language this way at all then?