this is not a direct response to your question but..'estimated 10M unique users'? this is an estimate for business you are starting? or are you building it for someone who already has traffic and expects to grow? if it's the former, I wouldn't worry too much about the scalability just yet..by all means use nodejs if it affords you luxury of using available resource skills and meets your feature needs..if it's the latter then it all depends on what is currently being used (for the tech stack) and why that's not good enough to scale