Cycle accurate emulation helps little with this era PC demos, because back in 1993 PC hardware performance variation was already massive. From 386SX-16 to Pentium 66 MHz, that's over 20x difference in performance.

> Cycle accurate emulation helps little with this era PC demos

It works, and has done for some time, surely. What more is there to add here above accurate playback?

> From 386SX-16 to Pentium 66 MHz, that's 10-20x difference in performance.

Yep, and some demos had specific requirements for not only minimal CPU but maximal because the assumptions inherent in small-code timing tricks would break beyond a certain speed or because of significant differences in relative instruction execution times (and sometimes the unpredictability of those execution times as the P5 architecture and some of its frankenstein-486-like competitors added branch prediction). Larger demos were more flexible as you didn't need the small-code tricks to squeeze into 4Kb or sometimes less, so 64K demos and larger could be more flexible wrt target CPU.

But cycle-accurate emulation has this sorted to: you just need the instruction cycle time accuracy to be matching a particular CPU running to the pace of a particular clock. And given the description of how this is being done (“The demo is run on an x86 emulator that records…”) I assume this is actually using cycle-accurate emulation!

I'm guessing the benefit here is that the overhead of playing back the demo on each client machine is lower when playing this recorded version, compared to each viewer's browser running the initial emulation live in the browser. That and doing something a new way was fun or otherwise intellectually stimulating for the dev(s) involved.