While some might argue the definition of a "dash" is to go fast (gotta go fast!) and thus be left untouched, I'd like to bring up an idea to make slows affect dashing speed akin to Kalista being slowed. Thematically the logic is sound but I don't know if that would be unhealthy for gameplay, what with the prevalence of slows and all.
When I saw a LoL reddit thread, a comment bringing up hyper mobility (+damage +utility), it made me wonder. I pondered and came up with this possible solution? Is a dash a "get out of jail (slow) free" card since you can still create the distance even during the duration of the slow effect?