It will entirely depend upon the fight and final tuning numbers. One thing of which you can almost certainly be assured, however, is that melee is going to get rotated more than ranged. With the addition of a new melee dps spec, the transition of one ranged spec to melee, and the fact that melee is arguably just more fun and visually appealing to play with the addition of the revamped visuals, there is going to be a pretty huge melee glut this expansion.
Overabundance of melee was already a problem for many guilds, and it's only going to get worse in Legion. If you're concerned about being rotated out, you'd be better off playing a ranged pure. This is assuming you're in a competitive guild that actually has a large enough roster where rotation happens. If you're in a semi-casual or casual guild, it's not going to matter.