I'd like to second his nomination. Bret would be perfect for a co-chair role.
I'd also like to nominate Mark Davidson from MITRE for the other co-chair position for the TAXII sub-committee. He co-wrote the current documentation and knows more about TAXII than we've had hot dinners (
http://www.oxforddictionaries.com/definition/english/more-%E2%80%94%E2%80%94-than-someone-has-had-hot-dinners).
He has been very open to new ideas, and has helped provide expert guidance for the TAXII community when its been needed. I see a combination of Bret and Mark as the perfect way to balance the tension between the need for change and the need for stability.