I created a post a while back asking for the same thing.
Think this is a great idea and would come in useful for every monzo user at some point i reckon
The issue, of course, is the exchange rate fluctuates and the final transaction value takes a few days to be confirmed. Whatever feature is added would have to stress “this is the current rate, not necessarily exactly what you’ll pay, so use as a guide only”.
That being said, I’d use this feature all the time as a quick yen to pound lookup when I’m buying plastic highschool girls from Japan
EDIT: Some examples of what I mean to avoid confusion lol: