Where automated form submission would come in really handy would be a competitive intelligence tool that scrapes an entire site (and subdomains), identifies what actions on which page trigger which tags, and stitched together entire marketing funnels. Being able to monitor a competitor's likely marketing funnels (and seeing which ones they keep over time and which change) would be incredibly valuable, and would necessitate knowing precisely which tags fired on every page, including post-submission pages.
You're right that universal tags and the event naming that you could parse from the JS could be very valuable, although it would be hard to normalize.
And you're totally right about stitching together marketing funnels for lead gen conversions, but I'm not sure how you would get that from an ecommerce setup short of making a purchase and refunding it (which might be impossible to do in many cases).
Part of me has wondered if there are any partnerships BuiltWith or others have with popular browser addons. I imagine if they snooped this somehow from users, it would be valuable to them (setting aside whether it is ok to get this level of data).
I played around with someone's open source version of BuiltWith (forgetting what it was called) a while back and it was pretty cool to see how it works. I'm not a developer (although learning to code), but I've done similar research manually as part of my job, so this is really interesting to me to see what else can be learned.
For example, if there's a publicly traded ad tech company and you know a substantial customer of theirs just removed their tag, or many customers did in a certain time frame, you could short their stock (or vice versa if you see huge growth).