In regards to cast time on physical ranged, it worked well on MCH as not every GCD had a cast time. If you proced Slug or Clean Shot, they would instantly go off, this coupled with rapid fire mean it worked well, whereas BRD (from what I remember) had everything on the GCD and even Empyreal Arrow had a cast time despite being oGCD.
So, with that, having some GCDs have a cast time would be fine. Just to throw around my thought, on MCH, make Drill and/or Air Anchor have casts, but leave the main combo and heat Blast Alone. BRD, Refulgent Arrow can have a cast, maybe Apex Arrow? but I feel that should be an oGCD anyway.
Dancer could be a bit harder to fit one in. They have obviously never had cast times, so maybe have it on Saber Dance? No idea,
However, in regards to this, it would be nice to have some sort of unique mechanic in regards to ranged physical. It can be something similar to cast times, but different. If, for example, you charged the attack instead. You can still use it on the move, and you get X potency, however, if you let it charge for a max of, say, 1.5 seconds, it can have X+Y potency. If they were really ambitious, they could have an attack that would take 2 GCDs to cast (but I forsee alot of problems with that). However, rather than it be either one potency or the other, have the additional potency increase through the cast time, so, just to put some numbers to give a better idea, every 0.5 seconds of casting, you gain 20 potency. So instant cast would be X, after 0.5 seconds it would be X+20, after 1 second, X+40 and if you get the full cast, X+60. It still keeps the cast time, but makes it different. This could also lead to situations where it would be better to cut the cast short so that you can fit on 2 oGCDs for a potential DPS gain.
Of course, it also adds in more potential abilities, like one that stops the cast, but still gives the full potency etc.
I should add, I really don't use the physical ranged role much except Machinist, so if anything is off with Bard and Dancer, that will be why.