there are many cases where you need to know the estimated transaction fee BEFORE you send the transaction. The "calculating feature" is already included in BitCoin, otherwise BitCoin couldnt tell you that you must pay a fee.
I would love to see a API RPC command for getting the estimated transaction fee. There are many cases for web applications on which you dont what that a users account balance gets negative. Especially because there isnt a option for blocking transactions which are making the accounts balance negative.
Is it possible to include such a command or will it already be in the next version?
ps: I dont like the solution with the extra fee account