Tabs commands are not registered at the workspace level but on the tab-bar, that’s why they can register a context-menu but you cannot register a keybinding.
One problem with registering this kind of command at the workspace level when in a view is that you’ll never know which view should receive the command (there’s one tab-bar per pane) except when you give the focus to the tab-bar.
My suggestion is to create you own command in your init.coffee file to trigger that event on the active tab-bar, something like:
Weird, I tried atom.workspaceView.getActivePaneView().find('.tab-bar').trigger('tabs:close-tabs-to-right') from a console at work and it properly removed the tabs. I guess the fact I had right-clicked in a tab prior to the console test had lead me to think it would work.
You can also put a class to the tab when triggering a command.
Yeah, I had been thinking it would be bad to muck with marking things as right-clicked without actually having performed any mouse actions, but I ended up doing just that. I added the following to my init.coffee: