The Xbox One could be a great way to mine Ethereum, but it all depends on how Microsoft chooses to implement it. The Xbox One has a lot of processing power that could be put to good use mining Ethereum.
However, Microsoft has not announced any plans to do so.
If Microsoft did decide to allow Ethereum mining on the Xbox One, it would likely be restricted to only allow mining when the console is not being used for gaming or other activities. This would prevent any slowdown of the console or interference with other uses.
Microsoft has also not announced any plans to allow users to sell their mined Ethereum for cash. However, if they did allow this, it would likely be through some kind of partnership with an exchange or wallet service.
At this time, there is no way to mine Ethereum on the Xbox One. However, this could change in the future if Microsoft decides to allow it.