Capn Notarious,
Lots of ways exist to drive a tail rotor, a small engine might be about 100 times more likely to fail than the drive shafting we now use. Various schemes such as hydraulic motors and such have been discussed, none are as reliable as the shafting we use.
Our worry is always tied to our beliefs, maybe not to the actual failure probability. The stats for drive failure is so remote, it does not even show up in the data, while the stats for CFIT account for 35% of all crashes, and 50% of the fatal ones. I wish we could all start a thread wishing for EGPWS instead of mechanical improvements to non-problems!
The Notar has lots of good points, and a few poor ones and no bad ones. It belongs in the playing field, but it is not a savior, IMHO. Customers will determine if it is the way to go. So far, the vote is a resounding no, otherwise Boeing would have held on to the Notar line when they sold the light McD helos off. The sales of the Notar family are far less than the competing conventional helos, I believe, probably due to the reduced payload and increased complexity, ie, less value for money.
"What Limits", while you believe that the NOTAR has more thrust than a tail rotor, you are quite wrong. The advantages of NOTAR are many, but strong yaw control is not one of them. Beliefs are nice though, they comfort you at night. Do not be shaken by facts.