Hey Raphael! Trails is when you click your delay pedal off, bypass it, but instead of the delay signal just cutting off it repeats and fades out naturally. It means that a pedal isn't true bypass, in that mode at least, but if done well it sounds great and is very musical rather than true bypass delay pedals where the repeats instantly stop when the pedal is bypassed.
I really love modulation on repeats.. I gotta put modulation in the box! I think it could be a cool option to have the modulation driven by the CV waveforms, that's one experimentation to do. I'll probably do a treble knob too... this delay will actually be set up a lot like the Cosmichorus so it's skeleton is basically ready. Buffer in, dry mix, pre-emph, compander, filter the highs, treble control, compander, de-emph, levels, wet mix, buffer out, Bob's your uncle.