Well, one downside to it that springs to mind is, the dispatchers will no longer have the benefit of being able to easily ID what service is trying to call in. At least it was fairly obvious if it was an FD, EMS or PD unit calling with the separate monikers.
My best guess would be that "Orange 911" is an attempt to sound more professional and/or homogeneous. To be honest, I never did like "718" anyway, it seemed cheesy using the call sign #'s as the moniker. I haven't been listening to OC for very long, but a friend in Sloatsburg FD who has tells me they used to use "315" on fire before they went with "36-Control". Well, I grew up with "44-Control", so I'm used to it and prefer that on the fire radio over anything else. Not that my opinion matters in the least lol.