Okay, here's what I'm saying (and before I go on, I used to be International Distributor Support Manager for Steinberg some years ago, so I know a bit about coding, processor use, etc. :O) I already have a GSP1101, with the beta 63 firmware that allows for Impulse Responses to be loaded. It sounds very good, even when compared to some more modern units, and it does delay trails pretty much exactly as you would like: The delay fades out while you are already playing the first notes of a COMPLETELY different Amp+Cab+Effects setup. This unit was made, what, 2006/7? Computing power doubles every 18 months at the same price, so being kind, I'll say you can buy SIX times the processing power at the same cost today. In order to achieve delay tails (and probably reverb too) you only need a pair of processors dedicated to this function so you can A/B between them (how you handle the rest of the modelling is up to you). The real cost of new products is R&D, Software Engineering, custom manufacturing of displays, hardware, circuit boards, advertising, marketing, etc. To include this from the design stage would cost maybe $50 in chips.
So, ten years later, with processing power costing 1/6th the price, and it still hasn't occurred to anyone that this is one of the most desirable features guitarists want?
Yes, I could jump through hoops with a lot of editing and programming to achieve this result using patches with 2 chains of amps/effects (wasting all that processing power in another way) that are designed ahead of time for a particular performance, but that destroys any spontaneous creativity, and means I'll spend probably tens of hours programming to achieve something essentially simple.
Finally, at this price point, I'm just not prepared to accept it, as I can get great modelling from (e.g.) an Atomic Amplifire, and use a GSP1101 for delay/rev effects, with a lot of spare change left in my pocket.
My HELIX has just been collected by the courier for return/refund. Maybe the future will bring one unit that can do it all.