The problem is a service like this lives and dies by the network effect. Without enough people using it, it's not attractive to new people. Services like Vimeo don't have that problem because they provide the same value to paying members regardless of how many other paying members there are.
Let's say you want to create an ultimate network.
Ask for $10K per month from each member and throw a party each month which will be host by Alicia Keys, Adele and many more top notch singers in the world. There will be 100 or so members. Aren't you going to be attracted in that 100 ? Not 10 gazillion. Only 100.
Sure we can't compare this exclusive network with App.net but believe me, Twitter having gazillions of people does not add any value to me.
It makes my day harder, because every day more shit is produced in Twitter and Twitter is focusing on # of people vs # of advertisement clicks. They don't care about me. This is the old T.V model and I don't have a cable at home any more.
I'm entrepreneur and a programmer. If App.Net brings in VCs, marketers, entrepreneurs and good programmers I'm in. I will pay $10-$20 p/m to be in that network. App.net will care about what their users think. They have to.
It's not about the # of people, it's about the value they create; the content they write, the links they share, the conversations they have.
I don't care if 2M 16 year old Justin Bieber fans joining to the network. No value to me.