The problem with such a button is that it would not be useful on its own. To facilitate a payment, the button must be linked to some plugin/action. Therefore, the issue is not how to create the button, but how to provide a payment gateway to other plugins/functionality.
To give you another example, I have also developed a payment gateway for Event Manager, and this lets you sell tickets to events using cryptocurrencies (although there does not seem to be much interest for this at the moment).
Anyway, my point is that the issue is usually not the button, but the integration with existing plugins. This is usually done via payment gateways. The button is usually rendered by the host of the gateway plugin.
In conclusion, the use case for e-commerce and subscriptions is currently covered via the WooCommerce gateway. If you have an idea for another payment gateway to a well-known plugin, please let me know.