You know, the more this goes on, the more I keep wanting to do this whole 'To Be Continuued' pack idea. The basic idea is to use the same mod list, but to completely change how they are used, from worldgen on up, to make a more engaging but still challenging 'expert mode' pack...
For example:
Starting off, you don't get access to Efab. That won't come for one and a half ages or so, because Efab will only be used for more complex crafting recipes, and the first age is called Sticks And Stones for a reason. The Smeltery will either be disabled or will require something you can't get yet to craft it, but it will NOT be an Efab half hour (or even ten minute) crafting BS time gate. I may just go ahead and disable it and use Immersive instead. Disable the Tool Forge while I'm at it.
Yes, the wood from logs and sticks from wood recipes are nerfed just like they are in Continuum, but the Hatchet from Tinker's (not the Mattock, just the Hatchet) has a psudo-treecapitator mechanic, to make chopping down trees faster, but it still consumes the same amount of durability (if not just a bit more) as chopping down whatever you just went through. This speeds up the wood production to make up for it, and increases the rate at which your axe will break, which is why the Sharpening Kits are going to be heavily pushed as a way to keep your tools running, because you can use them in a crafting square on the fly to fully repair a broken tool. Flint is probably going to be the top-tier tool material, although Cactus and Paper and Wood and Bone are all other options for making parts out of.
Oh, and Charcoal can only be made in a Coking Oven, so I hope you either find coal or find some of the other ways of making torches. This limits the 'five minutes in and I already have a branch mine and all the resources I could ever want' aspect of Minecraft, because lighting alone will limit the expanse of your branch mines. Ore smelting in regular furnaces is also disabled. Other than some food cooking, the regular furnace is mostly going to be a component rather than a machine. Iron becomes a Tier 2 material, meaning you will need to obtain Bronze or Brass before it is able to be mined. Nickel may also be found within ore deposits as an uncommon secondary find.
Oregen is also going to be quite different. While the total amount of ore in the world is going to be about on par, it will be found in deposits rather than scattered about. I think I can also make it spawn an ore of the deposit type at surface right above the center of the deposit as well, which can help locate deposits. The intent is not to hide the ores, but require exploration to find them. As long as you explore, you shouldn't have many troubles locating them. Obtaining them may get a bit interesting, though. Diamonds and Emeralds, for example, spawn in obsidian-encrusted geodes, so you'll need to find a way to crack that in order to obtain the precious gems within. Copper and Tin are going to be relatively easy to get to. Redstone might be a bit more problematic as lava tends to be found within Redstone deposits (yes, I'm being kind of a jerk here, the restone ore deposit in CoFH is going to have Lava source blocks as an uncommon secondary spawn), while Lapis are found in geode like deposits under wet biomes. The Lapis geodes tend to be large-ish, but not common. Gold deposits will have Platinum as an uncommon secondary spawn. Lead and Silver will be found in Galena deposits mixed in roughly equal quantities. All of this will be telegraphed to the player via the quest log, and you can occasionally find surface ores that might hint at what lies beneath.
Exiting Age One: Sticks and Stones will be done with creating Immersive Engineering's Coke Oven and Alloy Smelter (which ONLY runs on Charcoal). This will lead you into Age 2: Brazen Might. And it isn't until about half way through Age 2 that the Efab is unlocked. The Blast Furnace is about two-thirds of the way through this age, and is required to smelt iron ore into iron (only using Charcoal), as well as smelting iron into steel (only using Coal Coke). All of the Smeltery recipes that produce tool components go into the EFab instead, requiring the cast and the molten liquid in a tank and about ten seconds. Smeltery unlocks, but all of the casting recipes are disabled, the only real use for the smeltery is to produce molten metals to feed into the Efab structure, and it does NOT ore-double. Also, all the Carpenter recipes get moved over to Efab as well. Expect your Efab to be quite large, with many different tanks with various liquids in them by the time you are done with this age.
How does that sound for the start of an Expert mode pack, as opposed to how Continuum did things?