I love Tesla, and do hope they come out with a cargo van that can be converted to a class B RV. I think that is coming in the next decade or so, but you have to remember that Tesla is currently struggling to meet their 400,000 reservations of the Model 3 small sedan, which are still being mostly hand built, though the robotic line will hopefully be up and running in the near future.
They're still a young company (by automotive measures) and have a lot on their plate. Musk is generally too optimistic with his timelines, but he still manages to deliver eventually. Looking forward to someday having an electric Class B.