After two days of work, the process of virtualizing my pedalboard has taken a big step forward with the emulation of my Line 6 DL4 in Mobius. You can get the scripts here, and Mobius itself is a free download. The process of moving my effects rig to a laptop may be a really bad idea, but it wasn't even a possibility until I got this running.
The essential functionality I missed from the DL4's looper is the Play Once button, which I think was inspired by the Boomerang loop pedal. If Play Once is pressed while the loop is active, the mode is armed and the loop will stop playing after the current cycle. If the loop isn't active, the loop will play once (huh!), then stop. Pressing the button while Play Once mode is armed will stutter the loop, restarting it from the beginning of the cycle, kind of like a skipping CD.
I hadn't realized, until I began looking for software alternatives, how much I've used these functions in my compositions and covers. On "My Foundation," for example, I use it to trigger the chords in the chorus. In a lot of songs, Play Once sets the loop to end, while I simultaneously switch my other effects off or on--something I otherwise wouldn't have enough feet to do!
Now, it's not clear if I'm an oddity or if I just haven't transitioned fully to the dominant looping paradigm, but most other people with this kind of equipment don't seem interested in these functions--and it shows in the tools they write. Loopy Llama is a fine enough plugin, but it's clearly been coded by someone who has either more equipment than I do or a very different musical approach. Mobius itself is itself an emulation of the Gibson Echoplex Digital Pro unit, and so it doesn't even technically have a "stop" function, just different modes of "mute."
Luckily, you can script Mobius, and it has an almost obscene amount of capabilities. The difficult part is overloading one button, so that it will trigger different effects depending on where the user is set, at the proper time (hardest of all). So while the other two are nice (having Record and Overdub on the same button saves space, as does Play/Stop), it's the Play Once button that caused me the biggest headaches. But I'm proud to say that it should work properly now, assuming that you let it use the InsertMode variable to store its state, and you don't have some weird quantize settings. It wouldn't be hard to change the script to handle that, but this is a good starting point.