I'm not sure I see the problem with Better Dungeons. o_O
If you look at it as something that needs to spawn in the Overworld, then yes, that's a problem. On the other hand, if it's taken as just "optional exploration content", then there's no problem with having to use Mystcraft to access it. In fact, that might be preferable to having it in the overworld, since it means it's unlikely/unable to get in the way of anyone's builds, and no one has to deal with the problem of everything being looted already. Bear in mind that Mystcraft's Ages are dynamically generated. So there's never a point where you have to worry about old generation getting in the way. When made, an Age will always use the most current generation rules...which I think is Quixe's point. If you only look at Mystcraft as a way to fast travel and gather resources, then sure, it's hax. However, it's also a powerful tool for setting up bases with
just the right surroundings, and for exploring without having to go out thousands of blocks to find the right biome/ungenerated terrain. Looked at that way, it's possible to say it would be an ideal use of Mystcraft, possibly both mods.
(Also, giving Quixe more things to do is in my best interest, so I don't get boredomslapped. XD)
As an alternative, what about the
Ruins mod maintained by AtomicStryker? He is apparently fine with private modpacks. It should be even less of a problem to have in new generation than Better Dungeons, since it
only adds structure generation, not new items or blocks. Again, though, I'm not sure either of these really does pose any problem. Unlike most mods, which are there to give you something to make/use, their primary purpose is giving you something to find/look for. Having to go out looking harder for their content would, as I see it, be considered a plus for either in most cases, since finding the added content is in itself the "payoff", rather than what you can do with what you find (though they do, of course, make what you find at least occasionally useful). To put it a different way, "It's about the journey, not the destination.".
On a semi-unrelated note, can we set up some sort of Mystcraft recycling service? I have at least one Age I doubt I'll be returning to, and I can't be the only one. It would be nice if we could turn in our unwanted Descriptive Books somewhere, and have those dimensions deleted something like once every week or two (books destroyed after, of course), instead of having Dim IDs and map data for places no one will ever go taking up space. Just a thought.