Explanation about plugins : currently i write plugin for "Any way to extend LimeSurvey with PHP", it can be extensions, modules or anything else. Then let's speak for "Question type" and "Question settings"

Current situation : plugin are easy to add new attribute (Question advanced settings), and add javascript for a specific question .

I think you're totally right : slider must be a question types and not a settings in multiple numeric .

Unsure for the 2 way of showing Yes/No or Gender ?
Or for the slider_rating for 5 point radio list : New question in the dropdown or settings for 5 point choice.

The good things about settings : same setting (and some code) can be used for different question type …

I have created a custom question theme for Van Westendorp Pricing in LS 3.x - github.com/tpartner/LimeSurvey-Pricing-Sliders-3.x

@tparner : we spoke quickly with Louis about "question template", and I think question template need a way to add "Expression Manager validation".

Somethink like "add automatically" a new Sub-question validation equation
I put a feature request : bugs.limesurvey.org/view.php?id=13727 :)

Yeah, EM validation would be cool.