I also have this in my thoughts for ages, but this year I decided to go ahead and build it while I learn Elixir.
Probably not, because this will be a commercial product.
Anyway I will have a free tier and I will give access for free to the premium tier for Open Source projects that are not commercial, and are a real project, not just some random repo.
Yes I will be looking for help in testing.
I will first open the project to Pioneers, aka the first users that will be accepted only by my direct invite, and that will have access to the premium tier forever for free with the condition that they will be willing to participate as beta testers. Each Pioneer will be able to invite friends until I decide that the product is stable for general usage.