But why with arrow keys? I couldn't figure out how to remap to tab and gave up on fish.
Edited to add: A suggestion is a complete command line based on the history. Completion looks at the disk for file names and the like, and only talks about the current "word".
If the '→' key is too far away from the home row for your liking, you can use Control-E instead, as long as you're at the end of the input buffer (it's the "go-to-end-of-buffer" command normally)