Dudes, seriously, the things you're suggesting are all fine and dandy. But FUN? Any HX technology by-product (in the widest possible way even) wouldn't qualify as "fun" in my book, let alone being a "twist".
An IR loading box capable to also load long IRs would be something I could possibly imagine, IRs can be quite some fun to fool around with. It'd also explain why people might be asking when it'd come to the Helix and why it possibly wouldn't make it.
But then, I think that's a rather niche thing not many people would be interested in, so perhaps nothing to suit Line 6's portfolio.
Same goes for any kind of guitar synthesis or whatever. Would be HUGE fun for me, people interested would love to see it in their HX familiy products, too, but it might not make it due to CPU limitations. But finally, again: Very niche.
A capture box would be something I'd like to see as well, but unless they really make it possible to capture anything you throw at it, it would be a nice thing to have, still not exactly "fun" (and defenitely no "twist").
In a nutshell: I've got no idea. I just hope it's nothing mentioned in this thread so far, because that'd make me scratch my head - as I simply can't believe anyone would classify any of these things as twisting fun.