As I understand it US fed supports Basel III.
US implementation
The US Federal Reserve announced in December 2011 that it would implement substantially all of the Basel III rules.[24] It summarized them as follows, and made clear they would apply not only to banks but also to all institutions with more than US$50 billion in assets:
"Risk-based capital and leverage requirements" including first annual capital plans, conduct stress tests, and capital adequacy "including a tier one common risk-based capital ratio greater than 5 percent, under both expected and stressed conditions" – see scenario analysis on this. A risk-based capital surcharge...
....As of January 2014, the United States has been on track to implement many of the Basel III rules, despite differences in ratio requirements and calculations.[26]
Source:
https://en.wikipedia.org/wiki/Basel_IIIIf you are going to have sub debt/prefs in your capital structure, you may as well make it count towards Tier 1 capital. They can decide not to call/convert the low coupon prefs, but if you are doing it for most of the prefs, you may as well clean up the whole thing.