ALLM - Auto Low Latency Mode
VRR - Variable Refresh Rate
Neither have anything to do with audio, they are video related, particularly game related. They, as well as eARC which is audio related are all part of the HDMI 2.1 specification however all 3 do not require HDMI 2.1 to be implemented, they can all be implemented within the HDMI 2.0b spec.
None would have any real place within the SP3 however the SP4 is another matter as a cutting edge processor but this thread isn't about the SP3 rather it's about the SP4.
A true HDMI 2.1 feature is 4k@120Hz as the 48GB data capacity is required which would more likely be a game feature only for the foreseeable future before being used for say movies, if ever. With the Xbox Series X and PS5 coming out this year these features can all be put to use. ALLM and VRR are already welcome introductions for gaming in 2019 and 2020 tv's along with G-sync and Free-sync (to date more for PC gaming) are are now becoming relevant for consoles as well growing the market
The issue to date is that receivers and SSP's have not yet adopted the features thus gamers, I'll use consoles here as an example have no choice but to send the video signal straight to the tv (to utilize ALLM and VRR) and use the console's legacy optical output to route the audio to the receiver or SSP. I haven't heard of anyone using eARC to route the audio from the tv back to the SSP for gaming but in theory it's possible to do it that way and again in theory you could maintain audio from games with LPCM, Dolby TrueHD, Dolby Atmos or dts:X soundtracks. Obviously using the legacy optical out denies the gamer the high res audio as only Dolby Digital and dts would pass through an optical cable.
As to Bryston continuing making state of the art hi fidelity equipment, don't forget, Bryston does not make the SP4

thus it's a very unique offering within the product lineup and obviously much more complicated than Bryston re-branding Torus power conditioners as BIT's.