Soren is a one-man shop, and he is very upstanding. If you order one, you will get one. I can't speak to back orders, and he does often get busy with his day job and can take a while to respond.
Please be aware that a Two-X upgrade should not be taken lightly, it is an intensive install and you should watch the install video at least 3 times before purchasing one. Take a careful look at the parts where his hand is in the way of seating the battery and wires. You will wish you could see what is going on in there, and it is frustrating to fit it all in correctly.
It is highly unlikely that you will build a product as safe and robust as the Two-X yourself in the time it would take for your Two-X to arrive, even if it were back-ordered. I ordered mine a few months ago and it shipped like 4 days later. I have about 1,000 miles on my Two-X now, and I love it.
Please also keep in mind that you will not have problems on pavement with the Two-X, but you will have to be selective when you go off-road. If you have float plates, check them out. Any trail which can put a gash in your float plates is a trail you probably want to avoid on a Two-X. I still spend half my time on mountain bike trails, but I have to stay away from the ones with steep, rocky downhill sections (i.e. some of the most fun trails).
All that being said, the Pint will probably be on sale on Friday for $850 - $900. Would you be willing to spend double on a brand new Pint? I bought the Two-X with the hope of having it bridge me until the XR replacement is released. As much as I did not like the install, and miss riding on the gnarly trails, I would install the Two-X again without question, if I had it to do all over again.
FYI, the OW app doesn't support Two-X. I am working on getting pOnewheel and Onewave updated with a software battery remaining approximation for people with Two-X and Android phones.