Today Herroom launched their Universal Cup Sizing initiative which aims to provide a uniform cup sizing standard among brands.
Their problem relies in most systems which differ in what is the next cup after DD.
UK goes something like this: DD, E, F, FF, G, GG, H, HH, J, JJ, K, KK
US varies widely depending on the brand and what they want to do with the DDD, DDDD cups, plus include the I cup which does not exist in UK for some strange reason.
HerRoom attempts to solve this by providing a unique cups table, that goes something like D1 for D, D2 for DD, the next one whatever it is, will be D3 and so on, just increase the D factor by the number of cups.
I can see how this helps Herroom's clients and the problems we also have here when a visitor needs a bra of size XX but is not aware that she may need YY on the next brand.
Add to that, cup sizing increase method is not standard as it isn't always increased by one inch. So it solves the problem for Herroom and the brands they carry but cannot be taken out in the wild since the problem still remains. Just take a look at Wikipedia's entry on International bra standards.
That said, I don't have an immediate alternative other than this site itself. I think that either something completely different needs to come up and become a standard (unlikely) or just move faster educating people in order to make more pressure and hope for the cowpaths we are making get paved.
PS: I hate that they're using the letter D, just perpetuates the "D is huge" myth.