I think the best fee schedule is pay-per-use. 1 sat fee paid to the relay each use. (Of course when 1 sat = 1 USD that could be lowered)

The problem with "paid subscription" over lightning is that bitcoin is a push system, not a pull system like traditional banking. There's no way for others to pull from your account, you have to voluntarily push it out and subscriptions are basically a way to make future work for yourself each month.

But pay-per use wouldn't be extra work, and you wouldn't be paying for usage when you're not taking advantage of it.