So many people have EInk readers now that the upgrade market is significant. I can't see why a Sony T1 owner would upgrade to a T2 for example, so Sony is largely targeting new EInk adopters.
A built in front light is an upgrade promoter and so is a higher resolution screen. A higher contrast screen might get some to upgrade, but Pearl's contrast is perhaps good enough already.
A flexible screen would be important to institutional buyers for schools, but would not be a upgrade promoter in itself. However Charbax's "ultra thin, ultra light and basically unbreakable" device would be awesome.