I'm curious why you want to. I think Improved Initiative is fine as it is (though I could be convinced that taking the bonus down to +3 might be a good idea), but in general think that too many feats that add stacking, mechanical bonuses are, ceteris paribus, worth avoiding. Too many of those feats make feat choices more difficult than they have to be, create more lopsided characters, and provide (in certain circumstances) an unnecessary disincentive for taking feats other that expand the character's abilities in more interesting ways.
(What counts as "too many" depends in your game, but I think that if you already allow a modest amount of the splatbook feats, you probably have enough.)