I already saw japanese fans theorizing about Mosa being Shirahsohi months ago, mainly due to the fact that in japanese Mosa speaks overly polite (nobody speak like this in real life)... and Shirahoshi is the only character that matches.
I wanted to make a thread but Shirahoshi saying she only had Megalo to talk to stopped me, but at this point I'm not putting this type of retcon past Oda