sap.uxap.BlockBase (https://github.com/SAP/openui5/issues/1853, https://github.com/SAP/openui5/issues/1804, https://github.com/SAP/openui5/issues/1884, https://stackoverflow.com/a/42799046/5846045)

<!DOCTYPE HTML>
<html style="height: 100%;">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Demo</title>
  <script id="sap-ui-bootstrap"
    src="https://sdk.openui5.org/nightly/resources/sap-ui-core.js"
    data-sap-ui-on-init="module:sap/ui/core/ComponentSupport"
    data-sap-ui-async="true"
    data-sap-ui-compat-version="edge"
    data-sap-ui-resource-roots='{"demo": "./"}'
    data-sap-ui-xx-component-preload="off"
    data-sap-ui-xx-wait-for-theme="init"
  ></script>
</head>
<body id="content" class="sapUiBody">
  <div data-sap-ui-component
    data-id="rootComponentContainer"
    data-name="demo"
    data-height="100%"
    data-settings='{"id": "rootComponent"}'
  ></div>
</body>
</html>

sap.ui.define([
  "sap/ui/core/UIComponent",
  "sap/ui/Device",
  "sap/ui/core/ComponentSupport",//https://github.com/SAP/ui5-tooling/issues/381
], function(UIComponent, Device) {
  "use strict";

  return UIComponent.extend("demo.Component", {
    metadata: {
      interfaces: [
        "sap.ui.core.IAsyncContentCreation",
      ],
      manifest: "json",
    },

    init: function () {
      UIComponent.prototype.init.apply(this, arguments);
      this.getModel("lazy").setProperty("/enabled", false);
      this.getModel("block").setProperty("/mode", "Mode_1");
      this.getRouter().initialize();
    },

  });
});

{
  "_version": "1.50.0",
  "start_url": "index.html",
  "sap.app": {
    "id": "demo",
    "type": "application",
    "title": "Demo",
    "description": "Sample Code",
    "applicationVersion": {
      "version": "1.0.0"
    }
  },
  "sap.ui": {
    "technology": "UI5",
    "deviceTypes": {
      "desktop": true,
      "tablet": true,
      "phone": true
    }
  },
  "sap.ui5": {
    "dependencies": {
      "minUI5Version": "1.46.7",
      "libs": {
        "sap.ui.core": {},
        "sap.m": {},
        "sap.uxap": {},
        "sap.ui.layout": {},
        "sap.ui.unified": {}
      }
    },
    "contentDensities": {
      "compact": true,
      "cozy": true
    },
    "resources": {
      "css": []
    },
    "models": {
      "lazy": {
        "type": "sap.ui.model.json.JSONModel"
      },
      "block": {
        "type": "sap.ui.model.json.JSONModel"
      }
    },
    "rootView": {
      "viewName": "demo.view.App",
      "id": "rootView",
      "type": "XML",
      "displayBlock": true,
      "height": "100%",
      "async": true
    },
    "routing": {
      "routes": [{
        "name": "home",
        "pattern": "",
        "target": "home",
        "titleTarget": "home"
      }],
      "targets": {
        "home": {
          "viewId": "homeView",
          "viewName": "Home",
          "transition": "fade",
          "viewLevel": 1
        },
        "notFound": {
          "viewName": "Home",
          "transition": "slide",
          "viewLevel": 98
        }
      },
      "config": {
        "async": true,
        "routerClass": "sap.m.routing.Router",
        "viewType": "XML",
        "viewPath": "demo.view",
        "controlId": "rootApp",
        "controlAggregation": "pages",
        "transition": "slide",
        "bypassed": {
          "target": "notFound"
        },
        "homeRoute": "home"
      }
    }
  }
}

<mvc:View xmlns:mvc="sap.ui.core.mvc" xmlns="sap.m" displayBlock="true">
  <App id="rootApp" />
</mvc:View>

<mvc:View xmlns:mvc="sap.ui.core.mvc"
  xmlns:block="demo.block"
  xmlns:uxap="sap.uxap"
  xmlns="sap.m"
  height="100%"
>
  <uxap:ObjectPageLayout enableLazyLoading="{lazy>/enabled}">
    <uxap:headerTitle>
      <uxap:ObjectPageHeader objectTitle="Switch Mode">
        <uxap:actions>
          <SegmentedButton selectedKey="{block>/mode}">
            <items>
              <SegmentedButtonItem key="Mode_1" text="Mode 1" />
              <SegmentedButtonItem key="Mode_2" text="Mode 2" />
            </items>
          </SegmentedButton>
        </uxap:actions>
        <uxap:sideContentButton>
          <ToggleButton text="enableLazyLoading" pressed="{lazy>/enabled}" />
        </uxap:sideContentButton>
      </uxap:ObjectPageHeader>
    </uxap:headerTitle>
    <uxap:headerContent>
      <block:MyBlock id="myBlock" mode="{block>/mode}" />
    </uxap:headerContent>      
  </uxap:ObjectPageLayout>
</mvc:View>

<mvc:View xmlns:mvc="sap.ui.core.mvc" xmlns="sap.m">
  <Title text="Mode 1" />
</mvc:View>

<mvc:View xmlns:mvc="sap.ui.core.mvc" xmlns="sap.m">
  <Title text="Mode 2!!!" />
</mvc:View>

sap.ui.define([
  "sap/uxap/BlockBase"
], function(BlockBase) {
  "use strict";

  return BlockBase.extend("demo.block.MyBlock", {
    metadata: {
      views: {
        "Mode_1": {
          viewName: "demo.view.MyBlockMode_1",
          type: "XML",
        },
        "Mode_2": {
          viewName: "demo.view.MyBlockMode_2",
          type: "XML",
        }
      }
    }
  });
});