I'm also hoping for better video support in the future. In one of the Q&As the team from Lumafusion was talking about Proxy Media which might come in the future. And sure, if iOS natively support ProRes, I would hope that LumaFusion will support it too.
But the whole support of different codecs is this a big mystery for me. There are apps out there (like Infuse or VLC) that can play all those media without any hick-ups, even though they seems to decode the media on the fly.
Even simple movies file like from a DJI Mavic Pro or the Osmo Action are causing problems with the playback when editing. I have to run "Optimise and Consolidate" a lot. And I'm not starting to talks about the best quality movie files I record with my Fuji X-T3.
Even tough I really like LumaFusion and the way editing with it works, I still think that there are some essentials missing...
So let's cross out fingers, that iOS 15 might bring some surprising new features and performance boosts.
Just my 2 cents....
I'm still very new to LumaFusion and am not too familiar yet with a lot of its functions and functionality but so far I'm seriously impressed with what it is and what it does for the platform it's designed for.
You will find with any editing software (NLE) that there will always be something that bugs you. For me personally, my expectations of LumaFusion are tempered by its price and primary platform. I've already come across odd stuff with it but these things don't bother me so much as LumaFusion, for me personally, is already doing stuff that I want. My main NLE on Windows costs over $1000 and it too has problems for my workflow. I've been using NLEs for almost 30 years and I've never found one that's perfect, regardless of cost. So I do understand your frustration.
As for the codec stuff. I'm still waiting on a response from Luma-Touch support to a bunch of my questions. For now though and from experience. I'd guess that anything on iOS that can play certain codecs or recognise certain containers/wrappers that LumaFusion doesn't. Is probably live transcoding on the fly, as you've suggested, or they may indeed have their own codecs. As I've already suggested, LumaFusion may well rely on system codecs, be that hardware or software. Again, the reason I've suggested that is because on MacOS, LumaFusion does edit ProRes and very well.
You also have to remember that something like VLC only has to play single files, LumaFusion or any NLE has to do a lot more than that. I dare say that LumaFusion could probably already play certain files that it doesn't, it most certainly feels like it has the power and capabilities to do that. But if those files couldn't be manipulated, editing, colouring etc. I'd think that could be a more frustrating situation than not seeing them in the first place.
This is why I'm surmising that if iOS becomes natively ProRes compatible, one way or the other, just as MacOS. Then LumaFusion may well support ProRes as a source codec option and maybe even without an update as it may well just tie in to an Apple API.
With regard camera codecs. Many cameras are going to be using H.264 and H.265. I suspect your Fuji will use one or both. These codecs can be packed in to MP4, MOV and a number of other containers/wrappers. They can have all kinds of GOP structures. Most are inter-frame, some are intra-frame. Companies like Sony and Canon modify these codecs further to their own preference, Sony's XAVC as an example and all its variations. Then there's the type of chroma-subsampling used. Bit depth etc. There's also unique issues that can be caused by b-frame structure and placement etc. The variations are quite endless as to what can constitute a H.264 or H.265 video file unless they adhere to some strict guidelines that make it (almost) a global standard, like AVCHD.
The point I'm making with all that is. With so many variations it's really quite difficult for any one NLE to be compatible with every variation of even just H.264 and H.265. As a for instance. LumaFusion will happily play certain files of mine that my $1000 NLE either struggles with or simply can't play. Unfortunately, these things are sometimes just down to the luck of the draw.
Anyway. As you've said, let's hope we see some extra functionality with iOS 15. I suspect that LumaFusion will always be compatible with what the basic Apple camera app on iOS can produce and if that ever becomes ProRes, then happy days. Although, I doubt there'll be much by way of a performance boost per se. I only say that because LumaFusion's performance is already way beyond what I would consider to be reasonably expected for such software on the types of devices it's designed for.