All we know is it's different this time and can take much longer. Due to changes on Google's side, adding a GrapheneOS release for the new models shouldn't be expected to happen within just a couple of a days as it used to.
On a general note, while Pixel devices are usually available in stock right after release, prices tend to drop significantly within a couple of months or sometimes even weeks. So, unless you can leverage significant discounts or vouchers, it's probably not worth it to buy them at their initial list prices.
Separately, the new generation is going to be a major change, with the SoC being sourced from TMSC this time. It has the potential to be a massive improvement in some aspects but can also end up being a massive disappointment: since the hardware is going to be very different to any of the prior models, it's very much like a first-generation design all over, making it more likely to suffer from issues, some of which will only be addressed in the following iteration. For this reason, it'd also be advisable to hold until actual user experience reports start showing up.