If you were using the CDN without SRIs, then yes, that would have been the most obvious channel. However, I don't believe the attacker ever set up for that and the URLs never resolved due to CloudFlare blocking it.
> there's been some pretty huge breaking changes
Unless you were using the legacy API, there shouldn't be any major impediment [1]. I intentionally tried to keep backwards compatibility as I hate doing library upgrades myself! Drop me an email - allan at the domain in question if you have any questions about doing an upgrade.
> It looks like newer versions of datatables don't import static files from the datatables CDN like this.
I rewrote aspects to use CSS styled elements in place of images, so there were less resources to load.
> Would it make sense to issue a CVE for older datatables library versions that could be susceptible to this attack?
Per the above, if you were using the CDN without SRI for the resources, then any version could have been susceptible. However, I've seen no evidence that the attack took that vector.