Getting a nismo sentra motor, trans, ecu. Possibly, a lot more is going to be really expensive compared to a custom setup. It would be easier to just buy the Nismo sentra - No one has really broke into the turbo realm with the Versa besides the Fox Marketing Versa. Bob did the supercharger route however, theres no date for a production bolt on kit yet. I still firmly believe a custom turbo setup is going to be the way to go. Fab shops build exhaust manifolds all the time. A custom manifold can be had for around $750, another $1,000 +/- for a turbo, plus custom intercooler piping, downpipe, injectors, and tuning. Making power isnt cheap.
I would still like to see more stuff produced for the MR18/MR20... Rather than swapping motors - etc.. so soon.