DNC, and by extension NIN already have 'caster mechanics.' DNC dance steps, and NIN Mudras ask you to do a series of zero damage 'do nothing' steps in exchange for burst damage -- kinda like PCT's Motif, and Muse system that asks you to take a 'do nothing' action in exchange for burst damage. I don't think, and I don't think they think that DNC should have walking casts as evidenced by DNC not having them in PVP unlike the rest of the phys ranged. DNC (and GNB) do have walking channeled abilities, which yes please add this mechanic to PVE as well -- imagine being able to move while using Flamethrower.