the august copy is a draft then, as it was still in consultation at that point.
You may be right about the outcome if anyone actually did take it that far, but at least some of the DNOs are definitely making these sorts of noises and pointing to that section of the regulations as their justification in situations where monitoring is showing that the local grid voltage is regularly being pushed above the 253V 10 minute average limit by solar PV systems.
Northern powergrid have resolved this for the time being by applying a 6V reduction across the entire network, so it's not likely to be an issue again for a bit, but I don't think they have further leeway to repeat this across the board reduction, and this basically is the issue that they were trying to resolve via the changes around local geographic area, but as we all know, these changes won't really have any impact on the issue, so I expect this to be revisited, and probably to start becoming an issue in certain areas with high levels of G83 systems on local transformers this summer - I wouldn't be surprised if one of the DNO's decides to find a test case on it to clarify this point tbh.
IMO though the wording re 'quality of supply' would cover the 253V levels as these are clearly specified in the ESQC regulations, so forms part of the legal form of the 'quality of supply'
Regulation 27 imposes requirements to give information relating to a supply and to maintain the quality of supply within certain tolerance limits.
Regulation 27 <snip>
(2) Unless otherwise agreed in writing between the distributor, the supplier and the consumer (and if necessary between the distributor and any other distributor likely to be affected) the frequency declared pursuant to paragraph (1) shall be 50 hertz and the voltage declared in respect of a low voltage supply shall be 230 volts between the phase and neutral conductors at the supply terminals.
(3) For the purposes of this regulation, unless otherwise agreed in writing by those persons specified in paragraph (2), the permitted variations are—
(a) a variation not exceeding 1 per cent above or below the declared frequency;
(b) in the case of a low voltage supply, a variation not exceeding 10 per cent above or 6 per cent below the declared voltage at the declared frequency;
https://www.electriciansforums.net/attachments/uksi_20022665_en-pdf.120341/
put simply, IMO any DNO would be on fairly firm legal grounds to object if they could show that one or more solar systems installed under g83 were causing the local voltage to regularly exceed 253V, and for instance insist that the invert settings were updated to prevent the systems exceeding 253V in these situations.
The fact they might not have done this much yet shouldn't be taken as an indicator that they aren't planning to do so in future if the number of G83 installations starts forcing the local grid voltages above their set limits in significant numbers, particularly in areas where they don't actually have the ability to reduce the tapping further or any other simple mechanism to solve the problem... at this point I'd expect them to start knocking on doors putting the problem back into the court of the sseg owners who's systems are causing the problems.
It's actually something that's easily solvable via the inverter settings to introduce a gradual reduction in output from eg 251, 252, 253V - certainly far simpler than the DNO having to dig up and replace their cable with a lower impedance cable... something that could easily be undone with a couple more systems installed anyway.