Currently I have more of an issue with the way the WW/BT cooldowns work in relation to using slam. for like the last 4 years it's been "never delay the use of WW or BT" but when they changed BT to a 4s CD they eliminated a lot of free GCD's we had before. Now it's actually more DPS to delay WW by 0.5s so you can get a 2nd GCD for slam.
if slam were to always be instant but with a CD I would be concerned about exactly how long the CD is, because if it ends up overlapping with a WW or BT CD a lot it's going to be even more clunky than it already is.
also as far as arms is concerned giving them another CD on top of 2 procs to juggle could make it harder to play for some people (me) but for those who rock at whack a mole it could be a pretty good boost.