Add options for checkbox lists in backend forms, which allow user to set, if options will be scrollable or is sorted to columns. For example:

Now, when options is more than 10, then options is scrollable. Options will allow user to define (for example) if is used this default type (scrollable), or new style - columns (1/3, 1/4 etc...)..

This feature sounds interesting though, quite frankly, I do not really understand, what exactly you are wanting to achieve. Could you maybe post a screen shot of what you want to have changed? You could for example hack a quick mockup of your idea. This way it's probably better to understand, what you were thinking of.

Or maybe someone else can help out here and make it a bit more clear (to at least me ;) )

For example, i made some changes in _field_checkboxlist.htm (@ modules\backend\widgets\form\partials\ )...

Removed condition for <?php if (count($fieldOptions) > 10): ?> ... Then is always visieble "Select all / none" options... on

placed condition above and added inline style for style="width: 33%;display:inline-block;"

Then output will be: http://imgur.com/7vOcZHp