So again, IANAL, but I think a lot of those games could switch from the 3.5 SRD to the 5.1 SRD if their material was different enough. I think 13th Age almost certainly is but they also have a lot of other material that was also under the OGL that they referenced and, because of the viral nature of the OGL, you're sort of stuck with it. I think you'd have to have like seventy products switch to the CC docs to unravel them and that's too much.
But I bet, almost any new product one made these days, could change very little and comform to just using the CC BY 5.1 SRD (or any of the other 5e SRDs).
For 13A 2E it's only ("only") 32 products, assuming their copyright notices are complete, a lot of which are owned by Fire Opal Media or Pelgrane Press, so that'd probably grease the skids if it got to that point. It is a lot to unravel, for sure, but if there is value in replacing the OGL with a stronger non-OGL license, it's not insurmountable (if WotC initiates it), which would benefit the community (but not WotC). For something as potentially muddy as 32 copyrighted products, that's probably less effort than re-"engineering" a product that derives only from 5.1, but that all rests on an unlikely hypothetical (that WotC cares to start the dominos), so maybe more 3.x-SRD-based publishers
should be interested in rebasing their product on 5.1. I dunno. I think the OGL v1.0a is fine as it is, though it's not up to the same standard as if it was written first in 2026.
And, I say stronger
non-OGL license, because...
You seriously would trust another OGL license published by WOTC?
One benefit of a newer, stronger OGL authored by WotC over switching to CC is that, if it passed the review test Morrus suggests, it would presumably fall under Section 9 of the OGL v1.0a...
Updating the License: Wizards or its designated Agents may publish updated versions of this License. You may use any authorized version of this License to copy, modify and distribute any Open Game Content originally distributed under any version of this License.
...and all companies benefiting from 1.0a could choose to publish works in the newer version without having to do all of that unraveling up above. But again, what incentive is there for WotC to publish a version of the OGL that provides the same rights as v1.0a, but in more concrete, obvious, defensible, understandable terms? Seemingly none. That's why they punted to the CC BY.
This is the kind of stuff that makes me still feel that we lost something valuable with the OGL fiasco, even if companies still enjoy potentially-incidental successes in the market.