Since we are given new skills for mounted combat, and that some classes have different skills, I think there will be shared patterns between different classes:
A melee DPS pattern for champions, burglars, captains, wardens, guards
A ranged DPS pattern for hunters
A tactical DPS pattern for loremasters, minstrels, rune-keepers
Or more likely there will be a mix and match between some common patterns:
A horse attack pattern available to anyone
A melee attack pattern available to champions, burglars, captains, wardens, guards
A basic ranged pattern available to hunters, champions, wardens (spears) and guards
An advanced ranged pattern for hunters only (or they simply get the same subset as champions and guards!)
A basic tactical pattern for loremasters, rune keepers, minstrels and captains
An advanced tactical pattern for loremasters, rune-keepers, minstrels
This way, everyone has three patterns, except burglars but I can't honestly image a stealth burglar on a big war horse...
I think that for the time being mounted combat is mostly a solo thing, so no need for heals, support or tanking. It's mostly a duel mode with different DPS skills chained.
I'm a lvl 35 guard and i think they can use both weapons shield+one handed weapon on mount. I also think they can use two handed weapon a well. I't looked cool in teaser attacking those wargs, uspeshly the champs and hunters but never saw the only saw a gaurd for one sec.I't looks cool