I don't tink Blender will become a pay for app, there are 1000's of free apps who's business model can be surmised in one word; Donate.

That and Blender also provide source code so you can actually take the code, recompie it and stick your name on it and charge money, which is lower than dirt IMHO, but the license for open source software makes for some interesting reading.

http://www.blender.org/blenderorg/blender-foundation/press/re-branding-blender/