From a design (i.e. balance) standpoint, it's not a good idea as written.
First, it mimics the racial feature that humans gain. That diminishes the value of playing a human making it less attractive for players. Plus, it allows human characters to effectively double-up on their advantages.
Second, if the majority of characters are likely to take this, then that means it's too good. As a rule of thumb, anything that's too good not to take is potentially unbalancing.
Comparing this to other feats that do something similar, my suggestion would be something like this:
NAME THIS FEAT
You learn the use of an additonal At-Will power as an Encounter power, even if it is not of your own class. You must still meet all prerequisites and requirements in order to use the selected power.
Special: You can select this feat more than once. Each time you select this feat, select another At-Will power.