It doesn't matter how you add extra restrictions to 1.0A content; a new section appended to the existing OGL or a whole new document (such as OGL 1.1). Either way is equally forbidden by s.2.
The biggest problem with your interpretation here is that the standard legal rule that contracts should not be interpreted in a way that renders any of the provisions superfluous or meaningless. The sentence immediately prior to the one you're hanging your interpretation on says "No terms may be added to or subtracted from this License
except as described by the License itself", which means terms
can be added, if done the way the license describes. And then the way the license then describes to add or subtract terms is Section 9, the provision for updating the license.
You are trying to argue that no terms to the use of the content can be added at all based on a sentence immediately following one that explicitly says terms can be added to the license, and additionally that Section 9, if not an utter nullity, is in all substantive terms a nullity.
I mean, maybe a court will agree with you. I don't know for sure, I'm not a lawyer.
But to me, the obvious reading of "other terms and conditions" in the context of Section 2, that accords with the rest of Section 2 and with the existence of Section 9, is terms and conditions that are "other" in the sense they are
outside the license itself. A random publisher cannot, say, add a notice to a product that says "The Open Game Content in this work can be used in accordance with the Open Game License 1.0a if and only if you first send us a billion dollars." and expect adherence. But someone taking OGC and using it in accordance with the OGL 1.1, well, that's using the content in accordance with the terms detailed in the OGL 1.0a, over in Section 9.
(Now, it's entirely possible that a court will rule that various possible WotC-favoring terms of a new authorized version of the OGL are invalid because they are unconscionable in a unilaterally-promulgated revision of a contract of adhesion. But that's an
entirely different thing than trying to use one sentence of Section 2 to negate the OGL's own provisions for modifying the OGL.)