Notably, Tekkit have decided to permanently ditch IC2 as of their latest modpack release. That's a pretty massive seismic shift in the community. Their argument appears to be that everything (
of importance) that IC2 and RP2 used to handle, other mods can now handle and do so better. Their new modpack just uses MJ for everything.
I'm not sure we're
quite at the stage where vanilla IC2 and addons are redundant, but we're rapidly approaching it. It isn't that IC2 and RP2 are bad mods either - they definitely aren't. But they've done what they wanted to and, crucially, have both totally ignored what other mods have done in the meantime. RP2's problem is its cripplingly poor server performance as it was never designed for use on servers, whilst IC2's issue is a sense of stagnation. IC2 fundamentally still
works though and is internally consistent in its features and behaviour. What it needs isn't a rebuild, or an overhaul - all it needs is a refurbishment. In fact once they sort out the issue with textures that has bogged them down for a month I suspect we'll begin to see IC2 begin a retrofitting process of development to bring it back "in-date". If the IC2 devs don't do this, however, the mod will fade into irrelevance as it gradually gets totally outmoded by a set of other mods with superior design decisions, innovations and drive. The question is whether the devs care, and they don't have to by any means. That Alblaka has basically disappeared or gone incredibly quiet doesn't help, either, but that's his business.
For those of you who may be interested in an IC3 (and I would be, actually), GregTech is arguably that IC3 hobbled by the fact that it has to piggyback on top of IC2 with all its features and thus its limitations. Thisincidentally is the main reason I fully support GT's forcibly overriding the recipes in IC2 and indeed other mods to achieve a sense of consistency with its own approach. You can tell that Greg is a professional game dev student - he approaches the problem the way an inexperienced professional game dev would. (What that says to you about professional dev work is your problem. ;P)
As repeatedly pointed out, Thermal Expansion is very much its own mod that does its own thing and in its own right is an excellent system all its own. For my part I feel it succesfully replaces IC2 even despite the mod author's objections to that view in that it provides me with all the features I actually want in my base starting out and in the long term. I have my ore yield booster. I have my furnace with sensible fuel usage and respectable speed. I have my faster furnace (the Induction Smelter) with further boosted yield and performance if I want that. I have my sawmill. I have my nifty system that generates liquids on demand and lets me take them in and out of containers. I have my space saving utility machines and an ice box.
I have felt, even as TE was in Ultimate, that I could - and did - say to my server users that if they wanted something basic that did everything they'd ever really want, all they'd have to do is set up a TE factory and they're set for life; they could ignore the rest of the modpack entirely and still have a relevant and potent base of their own. I still feel that's true - and it's only getting better over time, the new stuff in TE looks awesome. You can also credit TE for overruling BuildCraft's crappy design decisions and making their power system not godawfully terrible and actually useful for people who don't feel obliged to cut themselves on weekends.
For ages the power system in BuildCraft felt like an afterthought only useful for powering itself until someone actually had the sense to
do something with it - and now many other mods have jumped on board as well, making MJ an incredibly useful backbone power system capable of supporting entire modpacks and oh look we've gone full circle in this argument. The only thing MJ is lacking now is heavy-duty power production and that's only because nothing has
needed heavy-duty MJ production up until now. (No, steam doesn't count.)
Got to say I agree with the Tekkit guys. IC2 doesn't provide me with anything I need anymore, and only GregTech gives it enough novelty to be worth keeping around at this point. The only reason you'd keep IC2 around now is if you just want to play IC2, and I suspect that's actually the issue for many people here. Nothing wrong with that, but it doesn't justify bloating a modpack with it if you're a pack dev and not a player.