If Greg just does bugfixes then there is no problem there, and to be honest I would not mind him adding some new content to base IC2 (yes I know people have said he isnt there to add stuff just make bugfixes ECT I'm just saying personally I would not mind if he did add some new stuff) that is basically ripped from his mod as some of it is quite cool (the IDSU for example) so long as the balance of the new items keeps in line with IC2 as a base, so an IDSU as example being a more expensive base IC2 MFSU and then when adding gregtech it gets the items costs back to what they are in GT.
Edit: Having a bit of a play with the (pretty unstable) IC2-Experimental builds that have some new stuff in, looks like some new items coming into play along with some possibly new reactor stuff, seeing plutonium as well as different forms of Uranium. However a lot of the commits on the Jenkins for that stuff seem to be from Thunderdark so not nececarilly greg adding that stuff, though whether or not it is greg adding it will definitely be nice to see more new stuff in IC2 looks like perhaps something new with ore processing is incoming. : )
Edit: Having a bit of a play with the (pretty unstable) IC2-Experimental builds that have some new stuff in, looks like some new items coming into play along with some possibly new reactor stuff, seeing plutonium as well as different forms of Uranium. However a lot of the commits on the Jenkins for that stuff seem to be from Thunderdark so not nececarilly greg adding that stuff, though whether or not it is greg adding it will definitely be nice to see more new stuff in IC2 looks like perhaps something new with ore processing is incoming. : )