The web pixel extension is bundled in with the Checkout UI Developer preview. The latter has been as of Oct 1 taken out of preview and is available for live stores. I had assumed hence that web pixel extension would also go live at the same time, but the documentation (https://shopify.dev/apps/pixels) still says that its in developer preview.
Does Shopify have a timeline for when the web pixel extension goes live? This would help declutter code on a lot of stores.