I want to have EB in vanilla/classic mode for the overworld. No new blocks. I might be OK with wasteland/CS -- and with the whole rain factor, I think I would -- but if I want to be able to distribute my world to others, I want only vanilla blocks generated on the overworld.

In ages, however, I want EB and Bunyan at full throttle.

To clarify: The goal is that someone that does not have EB can still use the world.

So maybe a config option per biome of Enabled/Disabled/Mod-Enabled, wherein the third option still allows EBXL terrain to generate, but does not do so automatically (meaning that another mod must "call" the terrain to generate it)...?

Per biome? I hope you mean per world/per dimension.

But it's more than just that. EB has a single config file for things like "classic mode", and this is basically asking for that to be a per-world setting instead of a per-installation-of-mod setting.

This will be a feature of the new 3.x architecture. Promise!

What I was thinking was that, while in some cases you might want to use mod generation only for all the new biomes, there are other times where you might want to pick and choose. A by-biome setting might take longer to configure, but makes up for this by adding more control. For example, if you wanted to keep in all the biomes that use only vanilla blocks in the overworld, while making (to use the Mystraft example) things like Red Rock, Cracked Sand, and Redwoods only appear in ages.

Going further, lets say I want "infectious" biomes to only appear as a result of instability, so I disable them fully and let Mystcraft's instability handler re-add them when appropriate. Meanwhile, the Autumn Woods, Green Swamp, Mini Jungle (because quicksand), Mountain Ridge, and both redwood biomes are restricted to mod generation, appearing only in Ages. Everything else is allowed in the overworld, because it blends in well enough, except for Marsh, which is disabled completely due to it being so hard to navigate.

3.x will have very configurable options giving this functionality as described.

Duplicate of #20