I don't have TF so not familiar with its existing looping features, but if I'm in total wish-list mode I'd like to see:
– at least 24-bit stereo looping.
– mutiple stereo loop tracks that can be BPM-sync'd to each other or not, independently toggled on and off, have independent volume levels, pan, forward/reverse playback, etc.
– very long stereo loop times available per individual loop, expandable memory via SD cards, to allow for creation of evolving soundscapes and textures (example: the Digitech Stereo JamMan's maximum length of a single loop is 10 stereo minutes. For some people doing phrase style looping that's an insanely long amount of time that they think nobody would ever really need, while others like myself doing live ambient soundscaping have maxed that out and wished for more…LOL).
– different "stop mode" functions such as Immediate, Run To End of Current Loop, and a Fade-Out mode with settable fade down time (either arbitrary, or as a percentage of the existing loop length e.g. fade out completely over the entire length of the current loop, 50% of the current loop's length, etc); I like jerra.s' idea of smooth cross-fading of loops for ambient soundscaping.
– tap-tempo combined with that awesome Eventide quality pitch-shifting, to allow for clean adjustments of tempo/time-stretching on the fly without going all kinds of Darth Vader or Mickey Mouse too quickly (as well as the option to do exactly that as well if desired ). I'm kinda visualizing a hardware version of what Ableton Live can do on the fly with multiple loops with software.
– the option to easily pre-assign a BPM and bar-length to a new empty loop slot via a value knob (by comparison, the Digitech JamMan Stereo only allows you to pre-determine BPM for a new empty loop via tap-tempo). This would work great for when stacking multiple effect units sharing the same BPM (and that might not have MIDI clock) and want to keep your audio loop sync'd to everything else i.e. delays, etc.
– along with that BPM option: both a visible flashing LED to the beat and an audible click that could go out to a separate headphone out without going to the main stereo outputs.
– MIDI control of BPM along with all the usual stuff of course, to work in conjunction with the tap-tempo/pitch-shift idea above.
– here's a total wish-list crazy one: some kind of multi-point envelope control of volume levels and pitch over time per loop track. For example, the ability for a very long loop to decrease its pitch slowly across the duration of the loop's length, or for on-the-beat fade-in/fade-out/gate/panning effects as the loop plays back. So, more creative options for weirdos like me.
– Loop or Single-Shot playback options.
– Easy transfer of stored loops to/from computer via USB.