Imo subscriptions aren't viable at all. For me to subscribe to something I need strong evidence that I will use it enough.
Automatic micropayments with a daily allowance seem like a much superior solution. They remove the friction of making the subscribe decision and keep the content creators in check by only paying for interesting content. Subscriptions can be easily forgotten or aren't annoying enough to bother to cancel them even if the provided content isn't worth it anymore.