Even once the DLL tools are out, don't expect Civ5 versions of the big Civ4 mods. For instance, there isn't going to be an FfH3, because Fall From Heaven was Kael's baby and he has no intention of rebuilding it for Civ5. So what you should be looking forward to are entirely NEW total-conversion mods like that, not just updates of your favorites from Civ4.
As to the original question, here's the thing. Combat in Civ5 is inherently tied to a target unit/city, with the sole exception of nukes, which target a hex and not a unit/city at all. Now obviously, we could change the UI to allow the user to click on a hex without a unit/city in it, simply by copying the code it uses for nukes, and if the only effect was going to be the pillaging of improvements on that hex then it'd actually be pretty easy to insert into the code (simply never start the combat event in the first place). So the actual mod for what you're proposing doesn't actually need the DLL to operate.
The problem with changes like this, or really anything more complex than simple XML edits, is that the AI has no ability to understand new options or significant changes to existing systems. So the above mod could easily allow the player to pillage at range through a ranged attack mechanism, but the AI would never use the ability. Obviously, this is not balanced, and so to make it truly work we need the ability to add new behaviors to the AI, and that requires DLL access.
Several of the existing mods add complex systems to the AI already, but they only work if they're "passive", to where the AI's behavior wouldn't need to change. For instance, in my mod I added SDI, a nuke-interception Project, that uses a custom bit of Lua code to function. Obviously, it makes a big difference to game balance, but one of the reasons it works for the AI is that its existence doesn't actually cause the AIs to change behaviors. If you're at war and have a nuke, and your opponent has a project that intercepts the missile half the time, you're still going to launch it and hope for the best. So, while the AI's behavior didn't change, this fact didn't give any extra advantage to the human player.
In other words, we don't need the DLL to do every complex idea. Just most of them.
