Your "slider list" concept isn't in HTML5 for the same reason there isn't a "checkbox list" that sets another checkbox to either checked, unchecked, or indeterm

Your "slider list" concept isn't in HTML5 for the same reason there isn't a "checkbox list" that sets another checkbox to either checked, unchecked, or indeterminate depending on the state of all the checkboxes in the list. The way you worded your blog post, it sounds like you think that implementing a "slider list" would be unreasonably nontrivial with HTML5 <input type="range">. Why do you think this would be so hard? You're just updating range inputs' values when one of the other range input's values changes. I don't see the problem.