This isn't new. The mechanic has worked since... Well, in NY experience, 1.08, which was probably about a decade ago already!
It all comes down to the physics. This may be connected to how there's a property of additional speed to jumping in Doom. Momentum carries better in strafes than normal forward and backward.
I assume it ties into how the movement works. Have you ever stood in one open area and just started alternating all the WASD keys to make Sonic kinda run in a circle? There seems to be a kick of speed when moving into strafes. This, combined with a specific angle that the spindash goes for, means that speed has no reason to stop flowing, and thus, continues to increase your speed.
It has speed run utility, but as there's a far bigger pool of maps compared to the days of 1.08, it requires someone to be really experimental, like with crawla-bouncing.
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