Yes, "anything is possible" 
That being said, unless others get excited and chip in, what I'm doing is unlikely to reach "production quality".
In a bit more detail, the FlexDash expects that each widget is a web component that has a certain interface (details still being worked out). So you can author additional web components. That is similar in effort to authoring new node-red nodes but different.
It may be possible to create a widget similar in spirit to the uitemplate node where the user can compose wimple web components without having to install tooling. That would be useful, for example, to create custom arrangements of buttons, indicator lights switches, drop-downs, text fields, etc.
Note that with FlexDash you really don't drag UI components into the node-red flow. Instead you send messages with a topic and payload to a UI state node. Then, in the dashboard itself, you drag a widget onto your grid and you attach it to the same topic.
