test.js

    /**
     * The resolved tool component to render
     */
    toolComponent: {
        value({resolve, lastSet}) {
            this.promise.then((Component)=> {
                lastSet = lastSet.get();
                if (lastSet) {
                    resolve(lastSet);
                }
                resolve(
                    new Component({
                        viewModel: this.props
                    })
                );
            });
        },
    },

tool component is rendered into stache using {{{toolComponent}}}.