I think the cool in mobile is to use the device without external things, so a TIC virtual keyboard would be nice, with only the keys necessary to code.
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The android version is very cool. And installing the Hacker's Keyboard we have a keyboard with arrows keys to move between the code.
A suggestion: In landscape as we have the keyboard above the screen, it could have a settings to define the total of lines in landscape where the screen will start to scroll. To avoid extra buttons on the screen the settings could be a text file in the sd card. This seems like a hack, but with this I could define a area that is visible with the keyboard on the screen.
This is just a suggestion, maybe you can think something better :)