I think popover and invoker commands with polyfills are already the way to go. The polyfills are small (and if you only want to use the "show-modal" invoker, it's like 10 lines to feature detect and polyfills just that).
Many good uses of popover really needs anchor positioning. There's a polyfill for that as well but it's not small.
Many good uses of popover really needs anchor positioning. There's a polyfill for that as well but it's not small.