Gmail FBL update

Last week Gmail started contacting ESPs that signed up for their new FBL with more information on how to set up mailings to receive FBL emails.
One of the struggles some ESPs are having is the requirement for DKIM signing. Many of the bigger ESPs have clients that sign with their own domains. Gmail is telling these ESPs to insert a second DKIM signature to join the FBL.
There are a couple reasons this is not as simple or as doable as Gmail seems to think, and the challenges are technical as well as organizational.
The technical challenges are pretty simple. As of now, not all the bulk MTAs support multiple signatures. I’ve heard that multiple signatures are being tested by these MTA vendors, but they’re not in wide use. This makes it challenging for these ESPs to just turn on multiple signatures. For ESPs that are using open source software, there’s often a lot of customization in their signing infrastructure. Even if they have the capability to dual sign, if they’re not currently using that there is testing needed before turning it on.
None of the technical challenges are show stoppers, but they are certainly show delayers.
The organizational challenges are much more difficult to deal with. These are cases where the ESP customer doesn’t want the ESP to sign. The obvious situation is with large banks. They want everything in their infrastructure and headers pointing at the bank, not at their ESP. They don’t want to have that second signature in their email for multiple reasons. I can’t actually see an ESP effectively convincing the various stakeholders, including the marketing, security and legal staff, that allowing the ESP to inset a second signature is good practice. I’m not even sure it is good practice in those cases, except to get stats from Gmail.
Hopefully, Gmail will take feedback from the ESPs and change their FBL parameters to allow ESPs to get information about their customers who sign with their own domain.