Given Belgium are scheduled to play England a few days later on 11th October at Wembley (AWs game being 8th), could it be played in London?
Even just a closed door match at an English FA training facility, a facility say that visiting overseas teams normally train at. AWs played Canada behind closed doors in Spain a few years ago, and that was well before Covid-19 was on everyone's lips.
Would of course need help of English FA, and other UK authorities. And their NHS no doubt has bigger issues than trying to help out re any health measures for 2 neutral football teams in Blighty.
Actually struggling to see the motivation of Belgium FA with bothering with this AWs fixture. They have 2 UEFA Nations League games scheduled in earlier FIFA September window (Denmark & Iceland). Then 3 games to be crammed into the October window now (AWs, 3 Lions & Iceland return game). By September all the Euro club leagues will be well under way, so their players in no real need of match fitness.
https://us.soccerway.com/teams/belgium/belgium/281/
Why bother with playing NZ? Unless is some fear, the September games will be canned and they want a little warm up for Wembley?
However see Hay as obviously being very very keen on this fixture. Putting aside any personal agenda stuff he may have, if this game doesn't happen, he's likely to go over 18 months without any contact work with his top Euro based players. From that Nov 19 fixture (vs Ireland) to say OFC matches in June 2021. Looks like OFC World Cup qualifying may begin March 2021. Any AW matches in that window would likely be just A League/Handy Prem guys. June 2021 being in the Euro club off seasons you may get some Euro guys willing to quarantine 2 weeks in an Auckland hotel, if that will still be a need to enter NZ.
But yeah basically opportunities for Hay to get his Euro & MLS based players together, pre late next year maybe, is going to be Covid challenging. If they can pull off the October Belgian game with a Euro based crew, they may even try do the same again in the following November FIFA window if any other Euro team has an empty match day slot. Also by November the MLS regular season is scheduled to be completed, so if by chance travel from the USA to the EU was an option (does appear unlikely) a few MLS players could be available.
Or even a November London game against a Euro based Socceroos. Aussie have some AFC fixtures scheduled for October & November - Kuwait (7th October), Nepal, Chinese Taipei & Jordan. Those games (if they happen) could just be A League Socceroo selections. What the chance of a hastily organised A League AWs verus A League Socceroos run around, post the August 31st Grand Final? Or earlier whenever Nix's season is over. Talay & Greenacre as honorary NZ coaches - Hay can link up some sessions by video.
https://us.soccerway.com/teams/australia/australia/156/
Lastly guys like Joel Stevens, N Boxall, Ryan de Vries, Niko Kirwan must be watching this closely. If they got picked for a fixture like this (even closed doors & is Belgium B) could almost be a career highlight for some. Plus great experience for all the youngsters like Garbett, Pjnaker, Wilkins etc (again if picked). Social distancing requirements may reduce the selfie opportunities though.