Yes, the 600 Sport & Indy 600 are great sleds, and if the 900 ACE hadn't come out, I probably would be riding the Indy.
A friend of mine has a new 600 Sport and after riding it and my ACE, I sure do like the torque, smoothness, and lack of 2-stroke smell of the ACE.
I wouldn't be surprised to see a replacement for the 600 Sport being a lower cost 900 ACE model, if that would be possible?
Only a month or so away and we'll see what WILL come for '15.
It would be interesting to compare the cost of buying and riding an Indy 600 compared to the 900 ACE. I assume the 900 is a premium upfront, but would cost a lot less to ride and then would be worth more 5 years old than the Indy. Not sure which would come out cheaper.
I'd be surprised if Yamaha doesn't put something out to compete with the ACE in the next year or two, unless they are just piggy-packing off Cat going forward.