I think vision-only L3 (AIUI you can read a book, but it can decide to alert you and ask you to take back over with some warning, or by pulling over on the shoulder if necc) on the current hardware and sensors is possible, but it will probably have to hand control back to the driver in various scenarios it can't handle, like bad weather or crazy emergency lane closures with flashing lights everywhere and bad road debris, etc. Also, we might still be a few years of software development out from getting there.
In that time, though, newer Teslas will probably get HW4, better cameras, and possibly high def radar in order to target true L4-5. If that happens before the L3-on-HW3 is perfected, I'm not sure they'll keep investing in it as they shift focus to the new thing, and then all of us that paid up to $12k for a system they thought would at least eventually be hands off L3 (if not more, depending on which public statements you believe) door to door across the country will have every right to be pissed off and demand some redress.