I designed my 70mm reel for the way I personally shoot 70mm (and have for about a decade now). I don't shoot an entire 15ft (or larger) roll ever. I shoot the number of frames I feel like (usually anywhere from 6-20) and then develop that length by cutting off the exposed strip and putting it on my reel. For me (and others who are also using it), this method seems to work super well.
@MattKing, my "someone" comment was only meant to say that I don't know specifically who, I did realize my mistake with the offline note that was provided. Sorry for that misstep. I saw other links in the thread and thought mine would be pertinent to the discussion is all. I genuinely wasn't a marketing effort.
Responding to your question about film strip length, my current reel accepts ~53" (132-135cm), which suits my above described shooting style perfectly. I designed it for personal use, but I got so many people asking for it that I decided to add it to my repertoire in my shop so it can be easily found and used by those interested. I fully accept that it may not be for everyone, but I'm really not aiming for a massive audience. It's a very niche interest. I niche within a niche, and I figure the convenience of being able to use Paterson tanks makes it very approachable for most home developers, without having to buy any entirely specific system to develop 70mm film.
I do periodically make further enhancements to my designs though, and increasing the strip length is something I have absolutely considered.