Since I’ve been slacking on structured training lately in favor of riding on Zwift Island I figured I’d try to do both last night. For me with an FTP set at 215 W (yeah…don’t laugh), It works out quite well to start a VO2 interval right at the start/finish line and push it through to the KOM finish point at between 225 - 235 watts (105-108%). Gives me about 5 minutes of work and about 4 minutes of recovery. Enjoyed it (kind of). Won’t work quite as well for y’all higher FTP monsters though. 
Jon Mayfield’s blog post had some interesting visualisations of crossing pain portals to begin and end intervals as part of structured training. Speaking entirely personally I’d see these as adding more credibility and versatility to Zwift than power ups and the the like. But that’s just me. I assume they’ll be coming soon.
I’ve experimented a bit using my Quarq as power source rather than Kickr and I think that works well for doing intervals. It takes away the sensation of going up/down the grade and sort of flattens out the island. Yes, you speed will increase/decrease when going up/down hill but I think it is easier to maintain a consistent power output that way.
I’m with Greg, I’ve gone with using my Quarq as a power source or switching the kickr into erg mode on my phone for interval workouts. The beta island is a bit short so the climbs are a bit short for a good interval session.
I did a ride the other day that I tried to do complete laps at around 110% of my FTP and the laps were just under 7 minutes. My FTP is 314 so I was trying to keep the watts at around 350 with slightly more up hill and slightly less down them.
The two VO2 laps ended up around 350W which is fine but it isn’t easy to judge without a current lap average showing.
Here was the ride listed on my Strava. http://www.strava.com/activities/244141983
The full lap at around 6 1/2 to 7 minutes is not bad for length and with the hills and other riders it does go in pretty fast compared to a similar block on TrainerRoad.
I imagine if they allowed you to have a pacer at a set ave. watts then you could just try and follow for a set time.
Stewart. That’s a good effort. I have an FTP of 311w and I know what 110% of that for seven minutes feels like. Hard. Did you ride a recovery lap before the second effort? Looks as though you did from Strava. I will give a lap at 350w avgerage a try.
Thanks Simon.
Yes I had a warmup for 10 minutes and calibrated the CompuTrainer then did one lap on Zwift with a bit of an effort on the climb then after the ‘on’ lap I had another easy lap before the second effort.
It was easy enough to judge the effort on the flat and climbs but the downhill sections catch you out and the power drops a bit.
On an interval workout on TrainerRoad in ERG mode it does seem a bit tougher at similar watts due to the resistance being constant which means you still need to push past the dead spots in the pedal stroke but around Zwift island it is more like Slope mode.
Doing it around the island is pretty good though and well worth giving it a go.
It’d be nice if they could add an ERG mode directly into swift island that you could toggle on and off. I too use my SRM for controlling Zwift in these cases, and control the Kickr from my phone.