Frankly I'm wondering where this comes from.
In IL-2 you can have 4 controllers at the moment.
I for one have a Saitek X-52 Pro and a Saitek TPM attached and once had an additional set of rudder pedals.
If I would have wished for more buttons, I could have added some game controller on top.
In my case with the 3 devices alone, it's been 13 axis, 23 buttons, 3 8-way hat switches and 9 physical switches.
I only have two hands and two feet, can't imagine what I'd need more for.
But even if so, and even taking custom cockpit designs into account, I'm still wondering...
The theoretical limit for a DirectInput device is 8 axis, 128 buttons and one native full-range POV switch.
With 4 devices this is 32 axis, 512 buttons or switches and 4 native POV hat switches.
Even if I take the cheapest custom chip for building such devices (JW24A8L, 4 Axis, 16 Buttons) this would give me 16 axis and 64 buttons.
Using the more sophisticated BU0836 chip you get 8 axis, 32 buttons and a hat switch per controller, that's 32 axis, 128 buttons and 4 hat switches in total!
So far I only know of 3 users having asked for this and from a technical point of view I'm afraid that there's a design flaw in a cockpit when you don't get along with the limits we currently have.
Best regards - Mike