Inability to Reinforce with Diplo Units

Topic says it. All diplo units are stuck in the cities they are created in and you cannot reinforce to another city with them. Secondly when you try: you end up diplo attacking yourself or an alliance member. This really makes defending new cities impossible from diplo attacks when first establishing them. This also goes hand in hand with the inability to place runes on any city but themselves.

I understand where you are coming from, but I think the vault takes care of the early stages.  If you are a new town and have more resources than the vault can protect, you may be doing something wrong.

One thing which would make this better would be to remove the diplo invulnerability inside their own city.

If it was possible for someone to target diplos at home to remove them that would solve the problem, changing the all or nothing of the diplo loss calc would also help.