What is the incentive for running a service for free? None. Copycats exist, but never last. A client is more than a set of features, there's brand, there's loyalty, there's ongoing support. If features were all that mattered Apple would not exist. 

I don't see subscriptions as charity. You pay for what you value, for whatever reason. 

We do need to scale to be able to pay full salaries though. Just as some play math:

$9 sub would require 1388 paid subscribes to reach $150k annual (decent for solo developer, 2 if you take a massive pay cut). This assumes a 5% conversion rate on all users (very generous I think). So let's say 1500 subscribers. This is about 27-30k active monthly users on the network - a 3x from where we are today. So.. not an easy feat, but certainly achievable. This doesn't include zap splits, donations, marketplace fees, any of that. Subscription-only would tough at this point, so I think it has to be a combination of things, or just work to scale the protocol. Scale solves a lot of problems (hopefully more than it creates).