I understand the technical difficulties. But the world is changing. Both the mobile environments and the desktop environments are changing. What is driving them is user experience and the perception of usability and familiarity. I don't know that the future will be a single unifying environment but I do think that the standard interfaces for the most common applications will. If you want to send an email you are going to be irritated if you have to figure out all over again how to do the one thing you do everyday. Even if you are familiar with the email programs on both machines, if they do not have a common look and feel then it is going to irritate you. Not just you but everyone who does these same common things. This is the kind of force that drives change. Someone will make a small change that makes it more seamless to move from working in one environment to the other more seamless. It will seam so obvious that everyone takes it for granted that that is the way it should always have been. The two worlds will have moved a little closer.
There is no question that data entry on a big desktop is more efficient than a small mobile screen but data entry will have to be done on the mobile device anyway. Whether you are gathering information in the field or making a last minute change to your spreadsheet. It just has to work. In the long run, the applications have to have the same features in both worlds. Then look at it this way, how many of those mobile devices have HDMI for playing back movies on HD screens? Just how sure are you that mobile devices are unsuitable for data entry when large (bigger than desktop) screens are so readily available?