Please yes, more access for modders. Especially access to basic values, such as maximum population, growth rates, empire research potential, even the pirate bonuses. These small things would make a massive difference in how much the game can be modded.
Eeeehhhh just don't overdo it ok? The Elder Scrolls is a bad example because of how easily the game breaks when you mod it.
You mean the part where the game has a huge lifespan, with a massive modding community and huge game expansion projects? As for breaking . . . that's more which mods you install, and how capable you are of interweaving them. Running a lot of mods on Elder Scrolls requires some actual talent, but it's quite doable with the right tools--tools which have been provided by aforementioned massive modding community.
If you're interested, send me a PM, and I'd be happy to discuss some of them and point you toward some sites that will make modding a lot more stable.