Ted, thanks for your detailed reply. I totally understand you.
Let me explain the "idea" a little bit more detailed.
I have developed some other softwares and online services and one of the biggest challenge I've faced is writing user guides/API docs for my softwares. Table of contents, indexing, search, rating, discussions and all other "parts" of this eco-system is challenging. I ended up using ZenDesk to power-up my knowledgebase/user guides but it's not user friendly. I am limited.
I decided to build my own "user guide" builder. It will be dead simple. There will be several "cool" user guide/API doc templates, it will be re-brandable and you will be able to point your own domain (ex: help.yourdomain.com) to the system. You will set your page templates and then start building the documentation. My service will handle the rest for you. ToC generation, index, search, rating, comments, statistics, integration to ZendDesk, Assistly, etc.
In exchange, users of my service will pay a reasonable monthly fee. I don't like free plans, therefore my monthly plan have a no-credit-card required 14-day trial period. Maybe I can add a very limited free plan with a badge at the bottom of user guides.
What I'm curious is whether this idea will work and I can find 10 paying customers...
I will follow Lean Start-up methodology on this project to lower my costs and quit early if it's not going to work anytime soon.