So it sounds more and more like Terminal 4 will be a skyteam terminal. Continental, Northwest, Delta and KLM will have flights there. Does AF fly there too? It would make a convenient connecting point if all Skyteam shared the same terminal. I also recall seeing KLM's Hollideck in T4....
Unfortunately, no one knows the minimum realistic connecting time because the flights and relocation haven't even started yet.
Based on everyone's opinion, just to be on the safe side, I did decide to stretch my connection to two hours rather than one. As NW booking engine says, 65 minutes might be sufficient but based on many changes ocurring in LHR, I don't trust it. Two hours would probably be better. As long as there aren't multiple arrival at the same time, I think it should be fine.
Jiburi