My company tried transitioning app subscriptions to alternatives outside the app stores and it was not worth it. Credit card fraud was a massive issue. It got so bad the payment networks (Visa, MasterCard) threatened to ban us from their networks.
Honestly not really when compared to the alternative. Our net payout through alternatives was closer to 60%. We experienced a bot attack one month where we actually lost money due to generating massive transaction fees on bogus chargebacks.
I thought Google shifted to a flat 15% anyway (especially for small app developers). It's really a no brainer for app developers then.
How would you download updates? Or even get updates notification? Who would support the infrastructure to download the app?
For 8$, i would simply bite the bullet. It's 27$CAD for a lifetime license damn it.