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

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

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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 …