Marlon/Bret/Jeff - I'm unable to attend the July 19th meeting otherwise I would make the following point in person.
I'm all for improving standards, especially if they are impractical, hard to implement, hard to use ...etc.
One of the critical items that must drive (any) standards at OASIS is a strong business use case that justifies the development of the standard or the improvement of the standard in the case of STIX 2.1/TAXII 2.1.
Just because we can do something doesn't mean we should do something.
Ultimately, interoperability and use of the standard is paramount over whether something is elegant or not. Companies or organizations will not invest in a new standard if it doesn't solve a problem that they care to solve. Or the existing standard is "good enough" that allows them to not invest in the new standard.
So I would encourage the TC to consider business use cases/priorities/sponsors that are concrete, that clearly identify why any technical innovation or improvement of the CTI specs is needed.
Otherwise a lot of work may go into specifying a great spec that no one implements or uses.
Regards