Pale Moon is an application working on a modified XUL platform code, that is a fork of Firefox with substantial divergence, especially for addons and user interface. The current version of that modified XUL platform (27.9.x) is a major refork of the core browser code to Firefox 38 ESR, which added HTTP/2, MSE/DASH, and JavaScript ES6 capabilities.
Otherwise, Iceweasel is just an application (like Pale Moon, Basilisk, Firefox, etc) that builds on top of the platform; focused to solve trademark issues and be used in all Firefox-based platforms. So i don't see the problem about use the "-classic" package name suffix for our rebranded version of Pale Moon when it's using an improved/modified version of the old XUL platform code. Basilisk is another application made by Moonchild, however it has been made to demonstrate the Unified XUL Platform (UXP) while it's under development, for that reason we're adding the "-uxp" package name suffix for our rebranding version of Basilisk.
Currently, Moonchild has plans to switch Pale Moon from their modified old XUL platform to UXP in long-term plans because a developed and maintained XUL-based platform is the only way that a XUL application (like Pale Moon) has any chance of surviving, with Mozilla abandoning this technology.
UXP won't be developed for Pale Moon's potential future use, it has been made for any future XUL application that will otherwise be dead in the water. Basically Moonchild is taking over the torch from Mozilla in developing and maintaining a platform for XUL applications of any kind.