It would be weird if it's something that FF users like currently, like the ability to go in about:config for example. It would also be weird if it's things that current users don't use, like pocket.
I want to get the subscription, but I hope the price and the perks are good and worth it, and at the same time not making it terrible to the free tier. Imagine they choose something that most people want but don't want to pay, and in the end FF loses users. I don't even want to think about it.
What is being hinted at is providing services like VPN and secure storage in the cloud from within the Firefox browser. Services that have a real cost in terms of bandwidth and storage.
It really wouldn't so much matter what the cost to benefit is to me provided the price was reasonable.