Good reply, thanks. Yeah kata for endurance is good too. Take very little rest between. We would sometimes do 5 different kata in a row for endurance and also for focus and concentration because as you get tired, form and even well learned sequence gets really hard. Great endurance.
But for interval training, I'll do a lifting set, immediately do a kata, another set,etc for 15 minutes. You are correct in that this is not a good way to practice kata per se, but seems to be a great way to do intervals. Also, as with any interval training, the amount of weight used is a little less.
I train karate solo now so this also a way to not forget these forms I spent years learning. When I want to tune up my kata, I just take a day away from the weights and focus kata. I may also use free style nunchucks or Bo staff as interval training.
A slightly less intense way to do this is to do three sets of say military press dumbs with minimal rest and then a kata before changing to another excercise like curls or pull downs. This way the amount of weight you can use is more in the body building range.