It depends on what you want the tractor to do. Running the engine can be done using free software so that problem is solvable. It is all the extra functionality

It depends on what you want the tractor to do. Running the engine can be done using free software so that problem is solvable. It is all the extra functionality related to semi-autonomous control which need to be built to create a fully open "modern" tractor which would be the biggest hurdle. Those functions may not be essential for small-scale or "hobby" farmers but they are so for large-scale operations whether they be using contractors or keeping the work in-house. So it would be solvable but who is going to do the work? Farmers tend to be risk-averse when it comes to equipment since they need it to work when needed - where "when" is often decided by external factors like crop and weather conditions, availability of supplies and help. When you're about to cut and bale hay you don't have time to tinker with your tractor since it has to be done before that cold front pulls in around 17.00 tonight...