As far as FRED is concerned, I foresee a few additions above the previously mentioned problems, that must be made before a build should recieve the stamp of 3.6.
1) as mentioned, fix Y-elevation, waypoint paths, & briefing animation bugs
2) incorporate support for jpg, tga, & dds for background images & ship textures
3) functional support for Kazan's multi-species additions
4) ensure all new sexps work properly (Hint, Goober, check your SG PMs)
5) Perhaps, patch in new model code to reduce load times, so it loads the ibx instead of the pof, but this is not an absolute necessity.
6) Support the higher number of background images that Lightspeed has been pushing for.
As far as I'm concerned, with the exception of 5, all of the above need to be completed before FRED can be considered on a par with FSO, in supporting the primary features.
Later!