WS2812 Led Strip Data Voltage Drop?
At least for the original WS2812 there won't be any significant voltage drop of the data line as long as the 5V is stable. Each LED is driving its own output line, there is no direct connection between DIN and DOUT.

See following statement of the datasheet (page 4):

Note: The data of D1 is send by MCU, and D2, D3, D4 through pixel internal reshaping amplification to transmit.

So in your case you only have to ensure that the input signal to the first LED of the strip is strong enough.