I think that the idea of many actors playing one character's doubles would be interesting, but it might be impractical on screen. We look at Grant and see Barry. If you have ten actors all playing a character with the same name, it just becomes different characters turning their head when someone calls that name.
Oh, absolutely. And, again, half the fun of parallel universes on TV (be it Sliders, Flash, Fringe, etc) is having different versions of characters played by the same actor. Seeing a meek and geeky Grant Gustin is fun because we know Barry as being fun and confident. Same with the other actors. There's less of a point to having Caitlin be Killer Frost if it's just another actress named Caitlin Snow playing her.
And if ireactions is right about the Snyderverse and the Arrowverse being in different multiverses, then it makes that whole point moot and the Arrowverse would function like Sliders where doubles are identical for whatever reason.
I just picture dialogue like this happening.
BARRY (weary from a fight with Zoom) - Who the Hell was that?
HARRISON WELLS (played by Robert Floyd) - That was Zoom.
CISCO - Whoa. Who are you, pal? How did you get passed our security?
HARRISON - I designed it. I'm Harrison Wells.
BARRY - That's impossible.
HARRISON - I'm Harrison Wells from a parallel Earth. The same Earth that Zoom is from.
CISCO - But you look nothing like Harrison Wells.
HARRISON - I'm from an entirely parallel Earth based on an infinite number of parallel choices. You think I'd look exactly like your Harrison Wells?
CISCO (embarrassed and sad) - Yeah. Kinda. I guess.
HARRISON - You know how many sperm -
CAITLIN (cutting HARRISON off) - Alright. We're all smart enough to know how that works. Let's just move on.