Not sure if you've visited the website or not, but this option is already there. If you select an altcoin, such as Ethereum, as I've shown in my screenshot below, the USD fiat value is available. If you pair it with BTC, as shown in the screenshot, it will show the value of the Ethereum value that you've indicated in the first pairing option (or vice versa; if you change the value of 1 BTC, it will show you the amount of Ethereum that it's worth).



Unless you were talking about having an option to show the value of multiple fiat currencies... Then actually, yes, this may be of value. But it's just that there are so many damn currencies, so maybe just the most common currencies, such as USD, CAN, EUR, GBP, INR, CNY, KRN, JPY.