There is a business model behind it but Layers itself will always be free and we'll be here to support it! We've been in the WP game since '09 and have zero intention of going anywhere anytime soon :)
Its the "Forever" part that makes me not want to use it as much, because I'm afraid of actually liking it and coming to depend on it, and then it going away. I'd much rather just pay some modest amount and know that I'm contributing to a viable business than hope that the owners have a business plan that works with "Free Forever"
I can assure you that in the WP industry paid for themes is not a guarantee for success. We know, we've been there with Obox Themes. We have a business plan that we are confident will keep Layers around for a VERY long time.