Seems that you want to have a tool which can translate requirements/test cases (written by business people with no experience in programming) into executable code.
In our practice FitNesse is not that tool. We started with FitNesse, and keep maintaining existing tests and even adding new when feasible, but these tests are written by developers, not business people. For them, we use formalized process (series of meetings and rules, not a software product) which requires business people to write documents with requirements and test cases (described in business terms), and developers/QA translate these into scripts for manual testing, or automated test, or unit tests, as appropriate. Important part is to communicate to disclose any misunderstanding and omissions, not to automagically translate document written in business language into code.
FitNesse language, even if user-oriented, is way too quirky and confusing for people without programming experience. And it is more hassle to write test in it than using plain old Python and Selenium.
Selenium gives you "open browser, click on stuff, check stuff" capability. FitNesse is another way to do it (and present results in Fit), using HTML generated from Selenium IDE. What you are looking for is (I think) test runner, like Jenkins, to run test written in Selenium.
I think that there is confusion what Selenium is, caused by complete redesign of what Selenium is :-) (I know I was confused). Very roughly:
- Selenium 2 does "click, check" by using each browser native automation capabilities (when browser responds to specially crafted URLs). Se2 does not inject any JS.
Selenese code generated by IDE (Se1) was pretty weak (no parameters, no loops - just exact replay of previous actions), so i.e. you cannot enter current date or date 2 days from now if page did not have a widget to do that. Se2 code is standard language (Python, Java, ++) you already know and love, easier to scale.
So I do not see any reason to consider FitNesse. Fit is considered dead by own authors and important part is the communication, not tools but of course it is your system and your project.