Let's start with Flight. The last video released by Microsoft is the first one that shows what appears to be in-game footage (the previous ones were clearly pre-rendered CGI "teasers") and shows a Boeing Stearman taking off. It is very interesting because it seems to use an evolution of the FSX engine, with better shadows and some nice touches like the blending between the runways/taxiways and the sorrounding grass and ground (unless it is a photoreal texture, but I do not think so). Apart from that, it seems very similar to FSX, so it may well be that Flight is an evolution of FSX, with better and more efficient engine and better graphics - and hopefully good chances to have (some) backward compatibility. And, some more missions (with more attentions to beginners) and Live features. That is what I hope, at least.
Microsoft Flight website HERE