Metal Slug Defense: What are the potential improvements in the future?

Recently, I am so addicted to this game - Metal Slug Defense. Right now, it is almost perfect in terms of the variations of the soldiers, skills, game play stages, etc.

But after rounds of Wifi VS PvP game, I think there is still room for future improvements.

1. Overflowing MSP

Please. Do something with the MSP... Thanks to the POW saving, my MSP value now exceeds 6 Millions... I am sure I am not the only one. I hope it can be converted into Medals or something.

2. Add more troops variation

Healing Units: Now, 99% of the units are meant for striking (except the Sandbag). If there is a nurse unit (or something similar) to heal the troops, the game play variation would be significantly increased.

Boosting Units: Perhaps if there are some units designed to raise the troops' HP, Attack Speed, etc on the battles, it will have more fun :)

Undermining Enemies Units: Am I playing too much Tower Defense Game? :p I wish to see something like 'freezing' the enemies to slow them down, both in moving speed and attack speed.

3. More Special Missions

If more unit types are introduced, definitely it would be great if there are more Missions to experiment on the new units :)

4. More Worlds and Areas

When will the World 4 or 5 be available?