Modern features are nice, but it should still feel like an Amiga editor. Which means for example:
shift-left = beginning of line
shift-right = end of line
shift-up = page up
shift-down = page down
ctrl-up = start of source
ctrl-down = end of source
It should also use Amiga-C for copy and Amiga-V for paste and not the control key.
Features:
A good search/replace function is frequently needed.
Also a macro function would be nice to record and repeat complex manipulations quickly.