I would pay for in-app purchases for:
3-color LUT control (instead of LUT presets, the ability to use 3 color wheels to create your own)
An extra video track (for iPad Pro users)
Video overlays (old film, film grains, flicker, light leaks)
Additional audio controls, like splitting mono to left/right channels or combining audio tracks to one
Additional titling controls (like scrolling credits)
Motion tracking of objects
Muting a video track
All separately, mind you. And don't be shy, these are pro-tools so make it worth your while. Pro editing software and plug-ins are expensive.
There can be more along the way, but by adding pro features as in-app purchases will give you a more sustainable business model and allows you to hire more developers to add more features. I'd rather pay a little more for app features than go to a subscription price model. I want to see LumaFusion succeed and grow. I can pick and choose what features I want based on my hardware's ability and my editing techniques.
I love the ability to edit while being mobile. Sitting in my backyard by the firepit with a cigar and beer and not being tied to a desk for hours is worth a lot to me.
If you need a boost to get these enhancements, offer a crowdfunding campaign. LumaFusion is poised right now to be the defacto-standard pro video editing app on iOS.
I would pay another 25 Euro for those features. Or even more. Just imagine what AdobePP costs - per month (this really suxx).
And I am not alone with this opinion.
Just develop a LumaFusion PRO version.
That would be nice.