Immediate Action metamagic feat. Could it be balanced?

[AustontheGreat1]

So I was wondering if it were possible to have a balanced metamagic feat which prepares a spell to be cast as an immediate action. Perhaps adding 5 levels to the spells. Would it be balanced?

[erikun]

Isn't this basically Quicken Spell?

Given that you only have one immediate action a round - and that you can't get more, unlike Attacks of Opportunity - I would think that an Immediate Spell metamagic feat could be reasonably balanced. Not sure what the appropriate balancing point would be, though.