At the moment, you can play Sea of Thieves exclusively on Xbox or a Windows 10 PC but things could soon change with Microsoft actively building their game streaming service. With an internet connection, Xbox Project xCloud will allow you to play your favorite Xbox games wherever you are, on any device and without downloading the game files!
At 2:41 someone is playing Sea of Thieves on a tablet with touch input and at 2:53 on a smartphone with an Xbox controller connected via Bluetooth.
It looks really promising and it sounds so awesome to be able to sail the seas on-the-go or when you don't have a computer with a powerful graphic card. I speak exclusively of Sea of Thieves but obviously a lot of Xbox titles would be supported because in the end, it will be like you are playing on an Xbox.
Public trials for the service should come in 2019, so I can't wait to have my hands on it! :D