Adobe has a history of including Digimarc within the PS product. Please consider shipping Lightroom 5 with a Digimarc plugin that supports automated application of the hidden watermark as part of the export process. It'd have to support and link to the Digimarc search service etc, but would save a lot of time for professionals watermarking their images.
I realise this idea might get handed off to Digimarc themselves, if so, no problem. Adobe certainly has more influence than I when it comes to things of that nature!