One of the most interesting things about the Bloomberg terminal that never seems to get mentioned in all the coverage and commenting is that its UI is optimized for users who actually take the time to go through training. In particular, everything is designed so that you never have to touch the mouse. If there are 20 choices onscreen, they'll all be numbered, and you type the number of the choice you want and press e…
I read another take on Bloomberg terminal's dominance.
A (potential) competitor might look at the Bloomberg screens and think they could recreate that more cheaply with Angular, React.js, or some fancy GPU accelerated DirectX. Maybe they'll have interesting ideas like beaming price charts to Google Glass, Apple Watch, etc.
However, that's just looking at the surface level.
The thing that's very hard to duplicate is the relationships that Bloomberg has built up over the years with all the data providers to get you ultra low latency data feeds. That's hundreds of golf games and 3 martini lunches the competitor would have to duplicate to establish the relationships Bloomberg has. The programming of the hardware and GUI would be trivial compared to the wheeling & dealing that has to be done.