Views support: Allow us to dynamically get nid for data relations

Dynamically selecting nids from some contextual or exposed filter would make this about a million times better.

I don't think this is likely to happen. The UI challenges around "just use arbitrary fields" is complicated to manage. Even on a site with a small number of forms (20-50), you'd run into a huge problem of listing all the fields on all those different forms. Restricting by NID first solves the UI problems for the most part. The only way I could see supporting a "dynamic" NID is if there wasn't a UI at all beyond a textfield for component ID (or maybe form key).

So although I think it's unlikely that we'll add support for any kind of wildcard NID, I made a separate, more easily built feature (from the UI perspective) over in #2036805: Use default views instead of hard coded listing pages, where we'd introduce basically a Webform-specific super-field where you only need to add a single field for all components in the entire form. Then when viewing the view, you'd be able to add/remove any component from that webform on-the-fly. Perhaps it's not exactly what you're wanting, but from a UI perspective that's much more likely to happen.

My dream is that components or fields would be reusable across multiple Webforms, so submissions could be aggregated and compared. I think I'm dreaming too big.
EntityForm is likely a better solution for anyone looking for this type of functionality.

Moving to won't fix. In your situation, the need to reuse fields across a small number of forms is probably better suited to Entity Forms like you suggest.