What I think will make things hard for mages (expecially healers) in roaming parties is not only the need to stand still (with all the server delay) but also the /facetarget thing.

Imagine being a CNJ or WHM, running around with party, which almost never stops, having to:
1 - chase party
2 - stop
3 - facetarget
4 - cure
5 - facetarget
6 - cure
(repeat)

with party members begin all over the place.

In a still party, instead, you position yourself where you can face all party members (like the whm does in the new dungeon video, if you check it, standing behind the mob) and just cure.