Its the only call to action on this page of the dialog, no harm in having a larger drop target (the textbox is already a drop target).
|mediawiki/core||master||+10 -8||UploadBooklet: Switch on showDropTarget in the SelectFileWidget|
|Declined||dchen||T118706 Conduct heuristic evaluation of image upload and insert flow in VisualEditor|
|Open||None||T115858 Design improvements for mw.ForeignStructuredUpload.BookletLayout|
|Resolved||Prtksxna||T115860 Show image thumbnail in both steps of mw.ForeignStructuredUpload.BookletLayout|
|Resolved||Prtksxna||T115721 Switch on showDropTarget in the SelectFileWidget of Upload.BookletLayout|
I'd suggest integrating the file selection and the drag&drop invitation in a single component, as illustrated below. In order to require less precision from the user, the whole dialog can act as the effective drop target.
In this way there is a clear entry point and users can make use of it as they are better used to. In the mockup from the description, we are surfacing too much choice for the user by showing three different UI elements.