Comment by carlmr

They have, kind of. Check out Gaggiuino. Sadly not really open source (Gen3) but you can get a cheap $500 Gaggia Classic and add fine grained control with an Arduino and display: https://gaggiuino.github.io

Then there's the really open source Rancilio PID Clever coffee project:

https://github.com/rancilio-pid/clevercoffee

Different machine, similar approach, a bit more DIY since you can't buy a kit.