I don't like the way watermarks works now. Why not make it available in the effects panel so that you can adjust it for each photo separately? Not every photo is the same and demands another approach.
Of course, there should be the option to turn off watermarks in one time for a certain folder/map. Or with the option of "apply only during export". Still better than exporting every image separately to get the right watermark for that picture. And, once exported you can't see anymore which watermark that was used. Therefore, i think watermarks within effects would be a great option for many users.
That gets my vote, as I'd prefer to be able to position the "signature" watermark to suit the photo. I'd like to be able to enable watermark in a Develop panel and set the location, opacity and color as another per-image setting. I'd also like an override switch in the Export panel to disable all watermarks for a specific export, just like you can override certain metadata being applied. I wouldn't imagine this would be an easy request, as it would require changes to the imaging pipeline as well as metadata, but it would be a nice addition.