WS2812B Without SPI

I know the ws2812b is rated for 5v but it should work with 3.3 as signal and 5v for vcc.

This hasn't been the case in my experience. There's some info about this in the neopixel docs: http://www.espruino.com/Reference#l_neop­ixel_write

As a starter I'd try running your neopixels off a LiPo battery (so 3.8v-ish). That lowers their input voltage requirements and tends to make them work great off 3.3v IO. If you then decide you need 5v you can look at level shifting and at least you'll know the hardware is working.

As @allObjects says, you can't do the simple input_pulldown and resistor hack on nRF52 though as it's not 5v tolerant :(