Exciting news ×2 today:
I've plugged the 4i4 in, put Focusrite Control 2 in a VM, connected the two together, and spent the weekend looking at pages of hex codes like this while playing with the controls to see what happens. It's good news! . I've found that the Gen 4 protocol uses (at least mostly) the same set of primitive operations that the Gen 2/3 use. That means that support for the Gen 4 can be done as an extension to the existing Gen 2/3 driver and it's not going to be a from-scratch thing (big whew!).
Also, @zeiktuvai has donated a 4Pre to this project! As support for that interface was going to be a stretch goal, I've updated the fundraiser goal to include the other interfaces and edited the description to indicate where we're up to.
Thanks again to everyone for their support as I continue working on this!
Here's the status:
Solo 4th Gen: will purchase this next if sufficient donations are received
2i2 4th Gen: have this, working on it next
4i4 4th Gen: have this, working on it now
Clarett+ 4Pre: thanks to zeiktuvai, will get this soon
After the above are complete, that leaves just these:
If you'd like to contribute to getting complete Linux support to these devices, please see the gofundme link in the first message of this thread. Thanks!