With the split from upgrades being accessible with tab to them being accessible with alt, I figured it'd be a good time to set "my" alt to one of the buttons on my mouse. (For compatibility with other Source games' sake, I have several of those buttons bound to numpad keys.) So I tried to bound Numpad * + T (T is my ability 1 bind) to upgrade ability 1. (Seems convenient to me: with my current setup, that would do a great job of avoiding excess Hand Yoga. Instead it simply rebound T to upgrading ability 1, unbinding my ability 1 key.
A little experimentation revealed that key-combo binds seem to be limited to modifier keys and tab. But you're going to be sampling raw keyboard events; you could let me bind whatever I liked as a combo instead. As-is, to get the behavior I'd want, I'd need to conditionally rebind my mouse to work differently specifically for Deadlock or do some weird config-file surgery (though admittedly I'm quite used to sticking whole state machines in my keybinds whilst playing TF2 Engineer/Spy, y'all could break this in the process of doing that planned update to avoid multibinds, so I'm pretty unsure that's a good idea in the long term).
A little experimentation revealed that key-combo binds seem to be limited to modifier keys and tab. But you're going to be sampling raw keyboard events; you could let me bind whatever I liked as a combo instead. As-is, to get the behavior I'd want, I'd need to conditionally rebind my mouse to work differently specifically for Deadlock or do some weird config-file surgery (though admittedly I'm quite used to sticking whole state machines in my keybinds whilst playing TF2 Engineer/Spy, y'all could break this in the process of doing that planned update to avoid multibinds, so I'm pretty unsure that's a good idea in the long term).