I think this is super new - there are only two apps that offer subscriptions that integrate with Shopify Checkout, and one of them launched in November it seems and is still in beta:
Awesome! Very exciting. I recently launched a small business which has a natural subscriptions element (https://narwallmask.com - a mask with replacement filters, which you may want regularly) but without subs integrated into shopify checkout, I decided simply not to offer it. Maybe now I can!
Can you say whether wasm helped make this happen? Seems quite plausible to me...