I think most people who ordered the car will be happy with demo cars being available, most people who didn't get a chance to order one before it sold out, or were waiting to test drive one before considering a purchase will obviously not be pleased.
However, in reality this car is a low volume production sports car in a very undersupplied market, so it was to be expected that it will sell out quickly, considering that ones in a "household appliance" category are on 6+ months long backlogs already.
In the States (who don't face the same regulatory challenges with having to sell the cars before 2024) the cars are available to purchase from dealers right now - at a 20-35% mark up. I'm not sure if that's any better to be honest, as most seriously interested parties got to order the car at a fair price in the UK.
Either way, I wouldn't be surprised if some, if not all, of the demo cars become available for purchase some time next year, however I would also expect the prices to reflect the current inflationary challenges and high demand. Let's not forget the total number of those is likely to be tiny to, only GR dealers with confirmed GR86 orders are said to be getting one.