diff --git a/lib/elements/dom-if.js b/lib/elements/dom-if.js
index 2b4f23c70d..70289708dd 100644
--- a/lib/elements/dom-if.js
+++ b/lib/elements/dom-if.js
@@ -182,7 +182,7 @@ export class DomIf extends PolymerElement {
     // Guard against element being detached while render was queued
     if (parentNode) {
       if (!this.__ctor) {
-        let template = /** @type {HTMLTemplateElement} */(wrap(this).querySelector('template'));
+        let template = this._templateInfo ? this : /** @type {HTMLTemplateElement} */(wrap(this).querySelector('template'));
         if (!template) {
           // Wait until childList changes and template should be there by then
           let observer = new MutationObserver(() => {
diff --git a/lib/elements/dom-repeat.js b/lib/elements/dom-repeat.js
index 7b0407d2e0..e330dce954 100644
--- a/lib/elements/dom-repeat.js
+++ b/lib/elements/dom-repeat.js
@@ -339,7 +339,7 @@ export class DomRepeat extends domRepeatBase {
     // until ready, since won't have its template content handed back to
     // it until then
     if (!this.__ctor) {
-      let template = this.template = /** @type {HTMLTemplateElement} */(this.querySelector('template'));
+      let template = this.template =  this._templateInfo ? this : /** @type {HTMLTemplateElement} */(this.querySelector('template'));
       if (!template) {
         // // Wait until childList changes and template should be there by then
         let observer = new MutationObserver(() => {
diff --git a/lib/mixins/property-effects.js b/lib/mixins/property-effects.js
index 1770585ac8..802586e937 100644
--- a/lib/mixins/property-effects.js
+++ b/lib/mixins/property-effects.js
@@ -21,6 +21,8 @@ import { PropertyAccessors } from './property-accessors.js';
 import { TemplateStamp } from './template-stamp.js';
 import { sanitizeDOMValue, legacyUndefined, legacyNoBatch, legacyNotifyOrder, orderedComputed } from '../utils/settings.js';
 
+const btp = window.location.search.match(/btp/);
+
 // Monotonically increasing unique ID used for de-duping effects triggered
 // from multiple properties in the same turn
 let dedupeId = 0;
@@ -2919,8 +2921,16 @@ export const PropertyEffects = dedupingMixin(superClass => {
       //     Change back to just super.methodCall()
       let noted = propertyEffectsBase._parseTemplateNestedTemplate.call(
         this, node, templateInfo, nodeInfo);
+      const parent = node.parentNode;
+      const nestedTemplateInfo = nodeInfo.templateInfo;
+      if (btp && parent.localName.match(/(dom-repeat|dom-if)/)) {
+        parent.removeChild(node);
+        nodeInfo.parentInfo.templateInfo = nestedTemplateInfo;
+        nodeInfo = nodeInfo.parentInfo;
+        noted = false;
+      }
       // Merge host props into outer template and add bindings
-      let hostProps = nodeInfo.templateInfo.hostProps;
+      let hostProps = nestedTemplateInfo.hostProps;
       let mode = '{';
       for (let source in hostProps) {
         let parts = [{ mode, source, dependencies: [source], hostProp: true }];
diff --git a/lib/utils/settings.js b/lib/utils/settings.js
index 84812d24f6..bc81c7bdf4 100644
--- a/lib/utils/settings.js
+++ b/lib/utils/settings.js
@@ -127,7 +127,7 @@ export const setAllowTemplateFromDomModule = function(allowDomModule) {
  * If no includes or relative urls are used in styles, these steps can be
  * skipped as an optimization.
  */
-export let legacyOptimizations = false;
+export let legacyOptimizations = window.Polymer && window.Polymer.legacyOptimizations || false;
 
 /**
  * Sets `legacyOptimizations` globally for all elements to enable optimizations
diff --git a/lib/utils/templatize.js b/lib/utils/templatize.js
index c29d96e012..e4f5ba4211 100644
--- a/lib/utils/templatize.js
+++ b/lib/utils/templatize.js
@@ -368,6 +368,7 @@ function createTemplatizerClass(template, templateInfo, options) {
 function addPropagateEffects(template, templateInfo, options, methodHost) {
   let userForwardHostProp = options.forwardHostProp;
   if (userForwardHostProp && templateInfo.hasHostProps) {
+    const isTemplate = template.localName == 'template';
     // Provide data API and property effects on memoized template class
     let klass = templateInfo.templatizeTemplateClass;
     if (!klass) {
@@ -375,10 +376,14 @@ function addPropagateEffects(template, templateInfo, options, methodHost) {
        * @constructor
        * @extends {DataTemplate}
        */
-      let templatizedBase = options.mutableData ? MutableDataTemplate : DataTemplate;
-      /** @private */
-      klass = templateInfo.templatizeTemplateClass =
-        class TemplatizedTemplate extends templatizedBase {};
+      if (isTemplate) {
+        let templatizedBase = options.mutableData ? MutableDataTemplate : DataTemplate;
+        /** @private */
+        klass = templateInfo.templatizeTemplateClass =
+          class TemplatizedTemplate extends templatizedBase {};
+      } else {
+        klass = class TemplatizedTemplateExtension extends template.constructor {};
+      }
       // Add template - >instances effects
       // and host <- template effects
       let hostProps = templateInfo.hostProps;
@@ -392,7 +397,16 @@ function addPropagateEffects(template, templateInfo, options, methodHost) {
         warnOnUndeclaredProperties(templateInfo, options, methodHost);
       }
     }
-    upgradeTemplate(template, klass);
+    if (isTemplate) {
+      upgradeTemplate(template, klass);
+      // Clear any pending data for performance
+      template.__dataTemp = {};
+      template.__dataPending = null;
+      template.__dataOld = null;
+      template._enableProperties();
+    } else {
+      Object.setPrototypeOf(template, klass.prototype);
+    }
     // Mix any pre-bound data into __data; no need to flush this to
     // instances since they pull from the template at instance-time
     if (template.__dataProto) {
@@ -400,11 +414,6 @@ function addPropagateEffects(template, templateInfo, options, methodHost) {
       // to not be since this is a vanilla template we just added effects to
       Object.assign(template.__data, template.__dataProto);
     }
-    // Clear any pending data for performance
-    template.__dataTemp = {};
-    template.__dataPending = null;
-    template.__dataOld = null;
-    template._enableProperties();
   }
 }
 /* eslint-enable valid-jsdoc */