I have two of Big Al's iSwitch single cell mosfet boards (fires down to 0.09Ω). He uses a 100A Vishay SIRA20DP and recommends a maximum of 40A to keep the mosfet from sliding off the board.The reddit guy posted some pics of the board, there are two AON 7428 N-channel mosfets for switching on board, those will most likely be the hottest components. They don't appear to have a heatsink.
There's a datasheet for those
http://www.aosmd.com/pdfs/datasheet/AON7428.pdf
but honestly I'm too lazy atm to dig out stuff from my uni time to remember how to calculate what power would require a heatsink to work safely and not let the smoke out at some point. I assume some 10 year old at eleaf did those calculations, added some kind of safety margin and set the safe operation at 50W. Probably 60W still would be fine but I wouldn't do above 70W for a prolonged time.
https://www.vishay.com/docs/76212/sira20dp.pdf