A while back I made https://gerrit.wikimedia.org/r/#/c/65346/ to add the "vform" layout (vertically-stacked using Agora buttons) to the HTMLForm class, and Matt Walker just merged it (thanks!). Forms using HTMLForm can choose this layout and then they'll resemble the Login and Create account pages.

As a demonstration the patch changes Special:PasswordReset to use this layout. It only takes a couple of lines to convert a form:
    $form->setDisplayFormat( 'vform' );
    // Turn the old-school line around the form off.
    $form->setWrapperLegend( false );

Cheers,