NOTICE: DOD rule change effective 11/13 (UPDATED for 11/19)

You cannot chase cas kill

No, these updated rules allow exactly that, CAS can chase CAS. However ground troops cannot kill CAS in dod.
Ground troops are also permitted to kill each other in the transit (DOD) zone.

Killing in staging area for all troops, both ground and air is prohibited.

You cant kill cas or trans over dod with a manpad or aa emplacement but cas against cas can?

That is correct.

I think staging areas will be easy to enforce. But you are now armchair theory crafting. In most cases that we've found around this specific context of "demarcated" staging areas, for this to be an issue, is a) the dod transit zone is so small, that an enemy would be able to even firing into a staging area. b) if a) were to be true, the enemy team has full authority to fire back without punishment, while the attacker will be admin'd.

If you as a human cannot in best-effort decide what is a staging area, the guideline I posted at the bottom of the rule applies to you. If you want to test that, I promise you will be met swiftly with a removal from the server.