I've always been very comfortable with out US Army construct of 11Cs (infantrymen who provide orgainc, hip-pocket indirect fires to the maneuver commander) and 13Bs (artillerymen who can pick up a rifle if need be, but are spciallized in Direct and General Support of Artillery fires.

It is easy to say "anyone can be infantry" (harder to actually do, of course); but timely, accurate, coordinated field artillery fires from mulitple units across the battlefield is a skill that takes practice, practice, practice. Throw your gunners into the lines under the same conditions that would drive you to throw your cooks and clerks. Sending artillery battalions off to war to serve as infantry just to ease optempo, or to give every commander "his chance" is, IMO, short-sighted.

(Oh, and maneuver commanders wisely guard their mortars jeaously. Weather and priorities may soon rob you of your air and arty support, but your mortars are right there with you, thick and thin. A mixing of specialites could alter the certainty of this command relationship; so Artillery commanders are respectfully told to "F-off" when they look too lovingly at a maneuver commander's mortars).