We have been using IC in one version or another for years now and we're about to start using the 1.10 version, but I would really like to see a few additions to the config:
(a) ability to turn off teleporting
(b) ability to adjust the base cost of teleporting in power
(c) ability to adjust the spawn frequency of ores individually for each ore instead of as 1 value
(d) ability to adjust the frequency of iridium spawning in chests - depending on how many other mods you have that spawn in chests makes building armor way too easy sometimes
(e) ability to turn off bronze armor for when you have multiple mods adding same.
I'm sure people could think of more, but the essential concept is that the more config you have to allow customization, the more people are going to use and enjoy the mod.
I would also love to see in-game documentation on all features, but that's another story 