FEATURE: Dismiss unread / new at top if more than 30.

app/assets/javascripts/discourse/controllers/discovery/topics.js.es6

@@ -108,6 +108,12 @@ export default Discourse.DiscoveryController.extend({
     return this.get('filter') === 'new' && this.get('topics.length') > 0;
   }.property('filter', 'topics.length'),
 
+  showDismissAtTop: function() {
+    return (this.get('filter') === 'new' ||
+           this.get('filter') === 'unread') &&
+           this.get('topics.length') >= 30;
+  }.property('filter', 'topics.length'),
+
   canBulkSelect: Em.computed.alias('currentUser.staff'),
   hasTopics: Em.computed.gt('topics.length', 0),
   showTable: Em.computed.or('hasTopics', 'topicTrackingState.hasIncoming'),

app/assets/javascripts/discourse/templates/discovery/topics.js.handlebars

@@ -1,3 +1,15 @@
+
+{{#if showDismissAtTop}}
+<div>
+{{#if showDismissRead}}
+  <button class='btn dismiss-read' {{action dismissRead}}>{{i18n topics.bulk.dismiss_read}}</button>
+{{/if}}
+{{#if showResetNew}}
+  <button class='btn dismiss-read' {{action resetNew}}>{{i18n topics.bulk.dismiss_new}}</button>
+{{/if}}
+</div>
+{{/if}}
+
 {{#if selected}}
   <div id='bulk-select'>
     <button class='btn no-text' {{action showBulkActions}}><i class="fa fa-wrench"></i></button>
@@ -24,6 +36,8 @@
         {{/if}}
         {{#sortable-heading sortBy="default" action="changeSort" order=order ascending=ascending}}
           {{i18n topic.title}}
+
+
         {{/sortable-heading}}
         {{#unless controller.hideCategory}}
           {{#sortable-heading sortBy="category" action="changeSort" order=order ascending=ascending}}