unrealistic to get anything close to all active users donating

It is quite realistic to get 100% of your users to pay. Just make registration conditional on the payment.

$10, $20 or even the $29 per year that I charge at Communick is not a significant amount of money for the average user. It is mind boggling that we got so used to “free stuff” offered by Big Tech that now anyone saying “Everyone using the service needs to pay for it” is seen as an heretic.