A company in my city created an EV conversion kit for any cars years ago. As they could not get certification for all models, they made a partnership with the constructor and managed to have certification for only 1 model (Renault Master, a utility truck) and now the company is controlled by Renault (the constructor).
They indeed killed the competition…
Unfortunately open sourcing is not an option without certification, cause vehucles will not be allowed to go on roads.
At least here in europe