Wow. I've been reading Thierry's axoloti work again, and I love this work: sounds great, definitely over my head, and I was google searching for BLEPs and DPWs in hopes I could learn something and apply it to my own work (and maybe one day get stuff happening on Axoloti, too).
I didn't think I would run across this (first?) SmashedTransistors post, saying 'I'm new here'. I kind of am too, as I keep busy and can only revisit axo places now and then. But I think I can answer the OP question.
Because I'm Chris from Airwindows, and I'm the one who did Slew2
It is NOT antialiasing, not really. I'm not nearly as good at antialiasing as Thierry. What's in Slew2 is a weird sort of technique for crudely oversampling a waveform and then doing weird things to downsample it back, and specifically what happened in Slew2 was accidental. It's a slew clipper, nothing more, but it interacted strangely with the 'antialiasing' that's not really antialiasing, and produced a big cancellation node right at Nyquist. Fun but I don't think there's anything in there that'll apply to real antialiasing (I'm better at wordlength reduction, still working out things about antialiasing).
I could open source (MIT license) Slew2 if you like, though the 'antialiasing' is a bit sad. But it did produce Slew2, so that was kind of interesting. I expect if you run sweeps and things through it, it will freak out in weird ways like the other plugins of that generation: I ended up going with a minimal-calculations model and putting all my attention on word length, and just doing plugins which don't challenge Nyquist so much. Of course if you're building raw oscillators you can't do that
oh, and of course Olivier is right, it wouldn't work as a general anti-aliasing solution for digital oscillators.
Anyway I just had to reply, to say, surprise! I am here, and already a big fan of Thierry's work. Who knew that my experiments would start such a discussion? I too am interested in the answers. Maybe I'll end up with real antialiasing after all