Drools.. yes pls.. For me I would have to say rarely seen from above. Is it possible to have both tall and wide? (oh god that sounds so wrong) If not I prefer wide.
The main thing that needs to be considered with this plugin imo, is how much terrain there is below the surface. I increased the amount to allow for larger caves as there wasn't really enough space for huge caves beforehand. This does mean that there is a lot more ground to explore and ore to find in chunks which may make it harder to find people. I have effectively done what has happened in this image: Compromising solutions could be to reduce the world border's size and/or increase the frequency of giant caves so a lot of the underground 'terrain' is just air. Also worth noting that the image I took of the cave showing at the surface is pretty much the highest possible cave and the lowest possible terrain.
I think a rare amount of caves would be good, but to compromise for the rarity allow them to be seen from above. There's always the risk of going in to find ore and finding it either a. Empty b. full of ore c. Empty disregarding the person who wants to kill you and take your items.
I'd like to get back into wastelands, would be a good substitute for LoL now that I'm back to school and I actually have to learn stuff. All this new stuff looks amazing.
It will very likely do so with the new biome changes, however, it may also fix some of the bugs when it comes to custom terrain generators, regardless, 1.7 is probably still quite a way away. Edit: The custom terrain generation is a feature supported and made available by Mojang (and likely built upon by bukkit) iirc, so it probably depends on what happens to that as well.