I'm quite busy at the moment, but I'll do my best to help out. I'm always interested in trying to improve pfSense - and the IPv6 code is ripe for further improvement.
I know you're already active in pfSense development, so it would be both inappropriate and redundant for me to give you a primer on pfSense development best practice. I just wanted to encourage you to consider opening a Redmine
ticket for this issue if you haven't done so already. Documenting the issue in Redmine can be helpful for everyone.
I haven't kept fully up to date with the dhcp6c and IPv6 changes in the master branch of pfSense which is, of course, what any improvements need to be based on. It may be that you need to address the architectural concerns I've previously noted in pfSense Redmine #5993-15
as part of your suggested feature if the refactoring I suggested there has not yet taken place. Unless your changes apply relatively cleanly to RELENG_2_3, I would think seriously whether it's worth the effort of backporting them considering the limited life remaining in that branch and that pfSense 2.3 is almost certainly closed to new features anyway.
on Github and you can always PM me on here. I'm perfectly happy to spin up a virtual machine to test anything you come up with; I can easily reconfigure my switches so that the VM has access to my WAN connections rather than the rack server than ordinarily runs pfSense here. I'm also happy to offer what input I can to the development process.