See bottom for updates with a great workaround
No suggestions but I did report this to them as a bug a while back. Basically the response is that they don't agree with Backspace therefore no one should be able to use it as their hotkey.
Here's my bug
This wouldn't be as annoying if there was a way to customize the hotkeys. Unfortunately that was also removed as they switched over to a new framework for managing the key-to-action mapping. Theoretically they'll bring back a way to customize it but I wouldn't hold your breath. It certainly won't end up in 3.16.
Here's two more bug reports for good measure 1 2
Bug I just submitted asking for a way to configure keyboard shortcuts
Ok so things have changed somewhat and I may have a solution if you're up to it. I have written a patch which returns the Backspace as up functionality.
I don't know what the procedure is for obtaining and building the source for a package is on Arch but as an Arch user you probably already know that part.
So here is the patch
--- src/nautilus-window.c 2015-07-31 10:18:29.313898480 -0400
+++ src/nautilus-window.c 2015-07-31 10:21:20.701351684 -0400
@@ -565,7 +565,7 @@
nautilus_application_add_accelerator (app, "win.redo", "<shift><control>z");
/* Only accesible by shorcuts */
nautilus_application_add_accelerator (app, "win.bookmark-current-location", "<control>d");
- nautilus_application_add_accelerator (app, "win.up", "<alt>Up");
+ nautilus_application_add_accelerator (app, "win.up", "BackSpace");
nautilus_application_add_accelerator (app, "win.go-home", "<alt>Home");
nautilus_application_add_accelerator (app, "win.tab-previous", "<control>Page_Up");
nautilus_application_add_accelerator (app, "win.tab-next", "<control>Page_Down");
I hope this helps
Another update: A github user by the username of riclc has figured out (quite ingeniously) that the keybindings can be altered by a nautilus-python plugin and has provided the code to allow for backspace-up here. This means no more patching and recompiling, just drop his script in the right place and you will always have backspace for up!