I don’t think they’ve been done much in the yo-yo world. I’d say the best example would be contact juggling. I think there’s a huge amount of untapped potential in terms of illusionary yo-yo play.
Definitely some untapped territory for creating an illusion via isolations. The only 2 tricks that come to mind are Mach 5 and Dr. Strange (the latter of which is surprisingly tough to do as an isolation, actually!). Those tricks are fairly ambivalent to string length. The illusion in Dr. Strange would probably be easier to pull off with a shorter string, if anything.
Indeed 
But there’s oh so much more!
Invent it, and they will come. Or something.
Lol yeah
54+ inches.
Does blueprint string come pre-tied?
Yes.
I use different length string for different styles of play, and also for different yoyo’s, but more often than not I use a fairly long string. I find a throw with a long string feels WAY different than a throw with a short string, and prefer the overall feeling. I love how big slacks & whips & suicides look as well. The biggest downfall of long strings though is the floor!! I’ve smacked the floor so many times over the years, and have actually dinged every single yoyo I own. People new to yoyoing should tie the string at about your belly button(or just above) to avoid doing this. When I’m throwing loopers I use a pretty short string, and it keeps getting shorter the longer I use it. Most often for me it’ll break at the slipknot, so I just tie a new knot & I’m off. They end up super short sometimes before I put a new one on.