CSS class do it for "Hide via CSS"
Hide completely ( No HTML) : actual hide attribute (except for equation)
Hide via Javascript / JQuery : only relevance currently .....

Is LS 3.X allowing to integrate this kind of feature more easily?

In LS3 you can create your own advanced question template and thus deactivate it by adding a hidden class, or deactivating it by jQuery.
So this is possible now.

LS2 have already easy solution … and if you need a checkox yes/no to add a class : it's already possible with plugin … No need LS3

But LS3 is better ;)

Unsure : each time i want to add a feature, i take 2 hours for bug report … ;)

In nearly every workaround thread in the forum we come to the point where people try to hide a question and use the option "Always hide this question". After that the workaround is not working. Then the discussion begins. Hide via Javascript, CSS etc.
Is LS 3 we now write "hidden" in the CSS class field, which is exact under the "Alway hide this question" button.
Way better than under LS 2.X. But the feature request is not obsolete ;-)

20180208.feature.hidecss.PNG (5,495 bytes)   

20180208.feature.hidecss.PNG (5,495 bytes)   

LS2.6X already have CSS class(s) … not related to LS3

Hidden by Expression manager (dynamic) can be great too .

https://github.com/LimeSurvey/LimeSurvey/pull/1258