Add a Soft Limit option

I need this feature too.
As a quick solution I've taken javascript from the facet's module soft-limit.js, modified it to use hardcoded limit, labels, selectors and used it in custom theme. But still need to exclude some filters.

  function softLimit() {
    // Soft limit.
    var limit = 15;
    var zero_based_limit = (limit - 1);
    var facetsList = $('..bef-checkboxes');

    // Hide facets over the limit.
    facetsList.each(function () {
      var allLiElements = $(this).find('.form-check');
      $(once('applysoftlimit', allLiElements.slice(zero_based_limit + 1))).hide();
    });

    // Add "Show more" / "Show less" links.
    $(once('applysoftlimit', facetsList.filter(function () {
      return $(this).find('.form-check').length > limit;
    }))).each(function () {
      var facet = $(this);
      var showLessLabel = Drupal.t('Show less');
      var showMoreLabel = Drupal.t('Show more');
      $('<a href="#" class="facets-soft-limit-link"></a>')
        .text(showMoreLabel)
        .on('click', function () {
          if (facet.find('.form-check:hidden').length > 0) {
            facet.find('.form-check:gt(' + zero_based_limit + ')').slideDown();
            facet.find('.form-check:lt(' + (zero_based_limit + 2) + ') a, .form-check:lt(' + (zero_based_limit + 2) + ') input').focus();
            $(this).addClass('open').text(showLessLabel);
          }
          else {
            facet.find('.form-check:gt(' + zero_based_limit + ')').slideUp();
            $(this).removeClass('open').text(showMoreLabel);
          }
          return false;
        }).insertAfter($(this));
    });
  }

This would be a great feature, one of the few things missing out of the box with Facets 3 integration with BEF.

The sample JS code there was very helpful for a temporary custom implementation, just a note that "form-item" is the class I needed on my theme as I don't have "form-check" (another option would have been "form-type-checkbox").