I think the devs have made it pretty clear that they are not going to change the spotting system. Love it or hate it, I wouldn't expect anything more than minor tweaks to it.
As for the viability of mobile artillery with the BF2 engine, we already have it in FH2: deployed mortars. You can place them anywhere on the map and the spotting system knows where they are. I seem to recall someone saying the problem with mobile guns, Wespe, Bishop, etc, was that they have to be deployed on level ground to function properly, and they didn't have a work around for that yet. I am not sure how they got it to work with the mortars, but they are much smaller.
But I could be wrong.