I discovered this extension while trying to resolve T193952 and for this ticket it would be interesting to have a button where the only action required from the user should be a click on the button, that will fill some text somwhere, save it, and thanks users for their contributions.
So basically, this is about skipping the edit phase. Preload can include dynamic wikicode and parameters, so I guess there could be a lot of other possible usecases.
As an aside, SemanticForms extension does do something like this.
As thiemowmde mentions, these types of features can be scary, lots of the methods for clickjacking/UI-redressing would also apply here, as users have a large amount of ability to customize page display with CSS.
Kicking out of our sprint, I see there are already features to accomplish the same goals. For example, the "Endorse" button on https://meta.wikimedia.org/wiki/Meta:Probox/Default does what we need.
We won't pursue this for next month's survey, the possibility raises more issues than it resolves.