Any ability that a battle frame can have can have an equivalent on an omniframe mecha. There is no additional limitation on what abilities are possible. In some cases the explanation and science of the ability will be different but the function can be identical.
Example 1: In firefall the medic frame originally had a "heal beam", in a mech game called hawken the technician mech has a "repair beam". They function exactly the same way.
Example 2: In firefall the firecat had various fire themed abilities. Nothing that could not be explained by flame throwers, thermal vents, napalm grenades and thermal grenades. (Have you seen the scorch mech from Titanfal 2?) If we replace firefalls old "hand out" animation with a little launcher or vent that opens it will look more "Weapon-like" but be effectively the same thing in gameplay.
In fact the lore of firefall's battleframes was that they used technology to create these ability effects. Why would being in a mech, which is also based on technology, suddenly take any ability options way? It wouldn't.
I cannot pretend to know what abilities will be decided on but I do know that they are not limited in choice.
TLDR. There is no limitation on Omninframe abilities.
as Ronyn said FF BF abilities can be made as omniframe abilities so i'm not gonnna post all the stuff (read abilities and abilities variations) that i did for ff. if any1 want to read about those they can download my work i posted in my thread about Evolving Enemies. here is just some stuff i came up with now....
Omniframe Abilities
Shoulder Mounted Launcher: weather in the form of a missile or mortar launcher, it fires a barrage of
said projectiles at a designated enemy or place. Variations may include: napalm or cryo missiles or
HE/ frag shells.
Shoulder Mounted Cannon: weather in the form of physical or energy, fires a series of shots at target
enemy or location.
Repair Drones: deploys a set of small drones to repair the Omniframe (either own or target friendly)
over a period of time
Night Vision: gives the player NV untill turned off.
Thermal Vision: gives the player TV untill turned off.
Mulit-Targeting Protocols: support ability. allows other abilities (like missiles or smt.) to target
multiple enemies or locations, dividing shots equally.
Target Tracking Protocols: support ability. allows other abilities (like missiles or smt.) to track a
target.
Head Vulcans: fires a burst of either physical or energy shots at target enemy or location.
Optical Camouflage: renders the Omniframe invisible for a set period of time. usable to hide the
Omni if the player needs to exit it for any purpose whatsoever.
Shield Dome/Wall/Deployable: deploys a specific type of shield to protect the Omniframe if the
player needs to exit it for whatever reason.
Shield Bits: deploys a set ammount of floating bits that intercept incoming attacks.
Assault Bits: deploys a set ammount of bits that attack nearby enemies. variations may include
physical or energy type of attacks
Pilot Abilities
may be bought as P.E.R.C.s (Pilot Education R(something) Course) for in game currency
Juryrig: repairs the Omniframe at the cost of durability.