1. Up to 4-beam/ballistic/ missile slot critical slots (4-slots for LRM20, AC20)
2. Mechwarrior4 1-,2-,3- beam/ballistic/missile slots
3. BattleTech TT critical slot sizes
4. Something in between.
What has been shown so far are the swapping of one Large Laser for two Medium laser which both fit the BattleTech and Mechwarrior4 criteria.
ie Large Laser is 2-slots or 2-criticals, Medium Laser is 1-slot or 1-critical.

Whats more interesting is finding out how ballistic weapons fit in the hardpoint system.
Ballistic weapons such as the AC10 and AC20 tend to take up alot more space than comparable beam weapons such as the Large Laser and PPC.
Side note:
It doesn't seem fair that ballistic weapons take so much space (in terms of size) than beam weapons.
The main difference between beam weapons and ballistic weapons should be the heatsink / ammo size.
My opinion is ammunition for the ACs should take more space and the weapon itself should take less space. (and maybe less tonnage).
For illustration purposes in TT rules an AC10 is 12 tons and 7 crits; perhap reducing ammo by half would be more appropriate;
For a Centurion, an AC10 (with 20 shots/2tons of ammo) take up 14 tons and 9 criticals; (assume that ammunition per ton is now only 5 instead of 10)
Change it so the AC10 now would be 10 tons and 5 criticals and ammo uses 4 tons and 4 crits to match the existing TT tonnage/criticals.
Also how does an AC10 fit between the upper and lower actuator; ie on a human's forearm and upper arm?
Maybe autocannon should be able to split up like an AC20.