Currently, I can't map anything to the <search> key (i.e., Google's replacement for the <cap lock> key) on my ACER C740-C4PE running Bodhi 4.0.0.
That is, Settings > Input > Key Bindings > Add/Modify does not seem to detect the key at all. I know from testing that Ubuntu 14.04 (since the behavior was the same in Bodhi 3.*) and 16.04 both detect this key as <Super> by default and use it to open the "Launch" menu.
I'd like to be able to assign it to the Moksha "Quick Launcher" (formerly "Run Everything"). I can also see how it could make for a nice compose key.
I have no idea how to implement this functionality, let alone how to do so in Bodhi/Moksha. My guess is that because it's not a "proper" <caps lock> key that it's not even detected by the system, but the kernel, Canonical, or both have a found a way to account for it.