It's unfortunate that Stripe has remained private. Both Square and Shopify IPO'd in the low single digit billions in market cap, allowing plenty of retail investors to tap into their growth.
Shopify is going to pull back payments from stripe. It's the only logical thing for them to do for them to boost revenue. They already ramped up the Shopify Pay branding and removed the "powered by stripe" cobranding on Shopify Payments. Stripe helped it along by not refunding payment fees on returns. Shopify's largest merchants are apparel companies who have high return rates.