I don't know if there ever will appear new units in MAN2, but some additional units that could be fun is:

1) Anti-sub frigate.
This unit blocks a radius of three hexes for enemy sub travel. It can fire only at a range of three hexes with 2 hp damage. Cost should be 4-5 depending on speed and hp. This unit would make it more likely to see carriers in operation again, as it seems these are rarely used anymore. A carrier with an anti-air shield and this frigate close by would be quite well protected. The shield is achieved by using ultra-high intensity sonar, of course

2) Submersible Carrier.
With a movement of 4, capability to hold 2 bombers and the ability to stay submerged this carrier would be able to survive to the battlefront unscathed. When submerged only torpedoes (Destroyers and Subs) may hit it. It's only drawback is that it must dive/surface before moving, so that it can not submerge after using it's bombers.

3) Fighter.
With a movement of 6 and damage of 2 this is a fast and hard hitting unit. I works like the chopper and has the same amount of hp. In addition it can not be hit by enemy choppers or bombers. It's drawbacks are it's price of 4 and that it can't conquer enemy capitols.

4) Heavy Transport.
Finally a unit that is capable of moving the colossal frog. It has a capacity of either a frog or three normal units, has 5 hp and even a 1 hp damage gun. Although with only a movement of 4 it will double the transfer speed of the monster within. The price of 4 makes it less accessible... Also this unit will not fit in a naval transport.


Well one can wish right

Anti-sub will be my favourite unit

I will try implement your ideas.

Other ideas:

1) Anti-aircraft instead of the air shield: AA destroys one bomber that tries to attack a unit within the AA's range. I don't know if AA should destroy before or after the bomber does it's damage.

2) Fighter (different from Try's suggestion): plane based in a capital (like a bomber) that intercepts enemy bombers trying to attack within the fighter's range which i was thinking should be 4.

3) Air transport: range of 12 flying capital-to-capital (like bomber). Can load one or two units. Basically very fast, but somewhat limited, transport of ground units.

Each capital could still only hold three planes at a time (fighters, bombers, air transports).

These are all rough ideas without specific costs or anything thought out.

I think your 3rd suggestion is very good. That would change the game a lot in some situations. It could though allow a player to stop a capture of a country by sending in a lav every turn to stop a enemy from capturing an ally, but this could possibly be sorted out.
The other two suggestions would result in losing a unit in your current turn, which I guess few would want. Maybe the fighter could instead block one bomber from entering it's airspace, so that three fighters could block a maximum of three bombers. With a price of 2 this could be a unit that would be used?

I agreed with you, Tamon! voted....