You can read how to send and receive WhatsApp message through email on my blog - https://abishekmuthian.com/send-and-receive-whatsapp-messages-through-email/ .
WhatsApp alone as a cloud service although technically possible is illegal due to copyright laws, but providing an android instance on cloud where users can install apps like they do on their device would be legal. I have talked more about app streaming in this video - https://www.youtube.com/watch?v=qjndVksuWrs .