I can see loading up 25% internal and taking drop tanks so that you can be nimble when you engage enemy fighters - I've done that too. But if you're going furballing and taking a mixed ord load, you'd end up dropping your bomb anyway.
With all the things they have to work on, I'd still have to put the ki-84 mixed ord WAY down the list of things I'd like to see done.
EagleDNY
$.02