I don't know where all the extended cut hope is coming from. Those who hated the original ending and are expecting something different from the extended cut are going to be disappointed.
Indoctrination Theory was not planned.
Per their FAQ, the endings will remain the same, only explained better with their repercussions via addtional cutscenes and cinematics. They will explain that we did not in fact destroy the universe, but only did what the catalyst says we did, per their original intent. There will likely be an epilogue where you see what happened to your crewmates.
Per BioWare's statements ME3 would have a lot of sophisticated endings and really no A,B,C endings. There would also be a lot of closure for those who sought it and all questions would be answered.
Yeah look how that turned out. Fool me once shame on you, fool me twice, shame on me. I'm not taking BioWare's word on anything until I see proof.
Mind you, I'm not convinced the EC will actually fix anything but I still have hope they're not telling us everything. The current ending is simply too ridiculous. No sane person at BioWare could think it's good and any attempt to defend it was obvious pr bs.
If I'm wrong they'll most likely try to explain the ending choices - and fail miserably of course - probably making the entire thing even worse.
Either way I haven't played ME since I finished ME3 and doubt I ever will again if BioWare fails once more with the EC.