There are no current plans to remake the Renegade single player campaign, GDI (Havoc) or the conceptualized Nod campaign, for the already prestated reasons: we'd rather get the game in a playable form first and concentrate on working on the internet multiplay.
However, if we do decide to change our mind in the future, be assured that we'd also inject alot more gameplay into it other than the 'run and gun' action seen in the original; Splinter Cell esque infiltration techniques, for example.
Unfortunately and unless authorised by the team directors, no mod' assets will released until we release the game in a playable and bug free form. If this policy is changed any single player work remains to be seen.
We (or at least I) am working out something along these lines, yes, although I am unsure if it will make it into the final first release.