I know that custom "Remote Actions" can already trigger Mac application shortcuts. But currently it's a tiny list, not usable in real life scenarios.
Instead, please allow a dedicated full screen space on the iPad that holds real size custom icons. Each icon would trigger a Mac shortcut. This would turn your app into a true shortcut dashboard.
Usage example: designers, CGI artists work with multiple complex apps and dozens of shortcuts. Really hard to remember them. Icons on the iPad should be the way to trigger them, not "CTRL+SHIFT+X+R". My proposal would persuade every designer / CGI artist to use your app, and quite frankly everyone would welcome this (Excel, music apps etc)
NOTE: each Mac app should have it's dedicated shortcut dashboard. So when we are in Photoshop, we only see the Photoshop icons, when we are in Zbrush, we see only the Zbrush icons etc. Icon graphics should be user customisable.