For tri policing:
-Drones have a limited control range and endurance - Motos can last for hours
-Drones aren't safe to use near large and small airports - Motors are fine.
-People along the race route probably wouldn't want overflights by drones, so you'd have legal issues - Motos operate on public roads, and so don't have issues.
-Drones require recharging, so you'd need multiple drones per site - Motos can be recharged in minutes.
-HD video (which you'd need to identify people) requires a TON of bandwidth, which you're not going to be able to acquire for a casual event like a tri. Motos have the decisionmakers on-bike, and so don't need transmission beyond a voice radio.
-In the US, the FAA has been taking a very dim view of drone usage for commercial purposes - Motos are obviously legal.
-If there's any wind at all, your drones are probably grounded. Motos can operate in any conditions that the competitors can.
If they cost more to police a tri, it's a non-starter. The tri community has clearly voted with their wallets that they don't give a fart about drafting - check out the success of IM despite the rampant drafting.
For commercial photos at a triathlon drones are good - you can keep them in one area you have permission to operate in, can take lots of photos before the battery runs out, you wouldn't need bandwidth beyond command/control bandwidth. Still have the FAA issue in the states though.
For Tour coverage, they're perfect - I wouldn't be surprised to see them in use for dangerous areas like descents or confined areas like the cobblestones. Grand tours make enough money to get around the legal/permitting issues.
STAC Zero Trainer - Zero noise, zero tire contact, zero moving parts. Suffer in Silence starting fall 2016