Currently there a couple of limitations with this approach. HTML widgets are built on top of Angular.js, and not on Angular, and some components, like Formly, are only available on Angular. We are working on making available the development of HTML widgets with Angular, but I cannot give you a date on when it will be available.
Another limitation, is that these components require additional packages to be installed into the angular project (not supported), but which may or may not be already available as part of the Thinger frontend.
When Angular is available we will try and compile a list on which components are available to use for an HTML widget