So Chainspell was an ability in FFXI for RDM. It was their 2h I believe that allowed them to insta cast spells back to back for a few seconds. Dualcast kinda does this. I think they could add Chainspell as a sorta upgrade to Dualcast by having it work on the procs you get. For example:

You Hardcast Jolt 2 > Dualcast Verthunder and get a Verfire proc. Since you got the Verfire proc Chainspell triggers making your next cast of Verfire instant but still allows you to Dualcast Veraero next. So as long as you get procs Chainspell allows your spells to stay instant.

Think it would work?