I like that idea a lot, a full screen mode for merchants makes a lot of sense.
Thought I was replying but was actually editing a previous message so in case you missed what I was saying.
The android wallet actually already includes that feature. It could use improvement as it is currently tied to btc-e and cryptys for the required data but once we are on cryptys a small update with our market id will turn it on and give you your balance in USD among other fiat's. Adding in more source options for BTC->FIAT would also be good. I personally would prefer the info from cavirtex where I'm Canadian.
This is lower on the priority list though but will eventually be looked at again and improved as we get more reliable sources of data.