We will always try to push the limits of what iOS and devices can do, so I do hope we can add more in time. Right now we are really asking a lot of most devices. I just got a new iPad Pro 10.5" (finally!) and it runs smooth as silk with 3 tracks of 4K, (as long as I used supported media types!) but it's not the most common device. We will keep up to date with what LumaFusion can do.
I also registered to give my two cents here. I just had to cut together a 9-teacher online choir and it would have been so much easier if Luma would support whatever the device is capable of. I had 0 problems with 6 videos and have a brand new iPad Pro 13 inch. Maybe you could increase the maximum amount of videos with better hardware in the iPads? Scale it?