Thanks - no plans to start charging as I essentially want it to grow into a community-based search engine.
Largely a proof of concept for now, maybe one day in the future might charge for indexing of private bookmarks, PDFs, etc, but those features aren't currently implemented due to technical complexity.
On a related note I'm interested to see how www.lumi.do does as this is one of the future feature possibilities I was thinking of for bkmrx...