Swifties or Mobis for celerity?

Basically I was wondering how mobis work with celerity. It's the rune that grants adaptive AP/AD for bonus movement speed. if you activate an ability for example (like warwicks R) will the added damage be calculated as the max movement or? after all you lose the bonus movement once combat initiates... but there may be an assassin or something that could use the mobi+ celerity