deauthorizing the use of OGL 1.0a for material released under OGL 1.1 would seem potentially doable and would be a statement made so that there is no confusion about whether certain content released under OGL 1.1 could be rereleased by others under OGL 1.0a (the question of whether OGL 1.1 would be legally considered a version of OGL 1.0a at that point might be in contention but outside that I think it would make sense).
I think it's perfectly possible for WotC - or you, or me, or anyone else - to publish a SRD and offer to license it to all comers on whatever terms we like. (Subject to general common law and statutory requirements.) And as I posted on the other thread, it seems quite likely that this is what WotC intends to do with its revised SRD.
But it would be confusing, in my view, to describe this as a "deauthorisation" of the OGL v 1.0a. What it would be, I would guess, would be (i) a non-authorisation of the new licence for OGL v 1.0a purposes (ie currently existing OGC can't be released under the new licence) and (ii) contractual terms in the new licence that make it clear that whatever form the new "OGC" takes, the new licence falls outside the scope of OGL v 1.0/1.0a section 9, and hence the new OGC can't be used under the current OGL.
The effect of (ii) seems clear enough (subject to WotC getting its drafting right, to actually do what it wants to do - although as long as the drafting is not terrible it seems a bit unlikely that anyone would actually try and test the limits in a way that WotC would care about.
The effect of (i), as I'm envisaging it, would be to mean that all existing publishers who want to reuse their stuff would have to reissue it under the new licence. Where publisher A's existing stuff is heavily intertwined with publisher B's OGC, that may be tricky. I don't know if WotC would care about the trickiness, and hence do something different from my (i), or not care. The most different thing they could do is try to set up a one-way door, so that everyone can bring everyone's existing OGC under the new licensing regime, but stuff licensed only under the new licence can't go back the other way. To my mind, that might be a bit tricky given the wording of section 9 of the current OGL, but I imagine WotC will be able to retain better drafters than me!