Thank you for your post.
Currently, drag and drop is handled at the FileMaker application level; not at the field level. To toggle this on/off for the applications, go to FileMaker Pro Preferences -> General -> Allow drag and drop text selection.
I recommend posting your request for field level access to the Product Ideas board at: Product Ideas
The Product Ideas board is monitored by Product Management and Development. All entries are read, discussed and considered for possible implementation in a future release.