To be replaced by what? Smart TVs, MediaPC's, etc most definately (I don't use Sky's STB for my viewing :-) ) but if you simply mean on demand via webpage then no. I can't stand the idea of not being able to control the content with a remote control.
My holy grail would be a single smart TV/MediaPC/Android,Roku etc. device application that can aggregate all the online/physical channels in to one program guide with the ability to record according to certain loaded parameters that the company can 'control' (ideally there would be no control but we know that won't happen). I hate having to flick to different web addresses or to load different applications to watch content.
Currently I do this with MediaPortal and can view all FTA/Sky channels in one guide, record anything I want and also view my movies, music and pictures using a single remote control.
EDIT: Another question, how do people remember all those programs they want to watch if they're spread across multiple providers with guides or are on deman only? If you can't set a reminder then you might miss something, especially if you're getting drip-fed programs as they're released.