I will start by saying I like to play alts, gives me some variety, multiple professions... one of those alts is a rogue and what I think Blizzard nailed with rogues in 5.x is the implementation of keeping up Slice and Dice. You blow your first combo to get SnD up, then next combo point(s) you use your main finishing move which refreshes SnD to maximum duration.
That is how I'd like to see 90 tier implemented in 6.0, we have a resource, at start of fight we use that resource to get our buff up (could be different for each spec), then for the remainder of the fight our buff is refreshed by casting a specific spell per spec. Those specific spells could be new spells in 90 tier, that ramp up based upon amount of resource used while at the same time refreshing the spec buff.