Without hacking the client you'd need collaboration from SOE (which would never happen due to their security concerns for the player's personal info held in the database) to make a gadget like that.

And you'd need a valid player account to actually check the marketplace... it's a task better suited to a full website rather than a gadget. That, and I can't readily conceive a situation that a gadget like that would be useful, that is within the TOS/EULA.

Far more useful would be these forums having an RSS feed that filters out invalid characters... the feeds from here are frequently unviewable due to faulty codes.

Having a server status report would be nice too... then I could make a gadget that showed server status, MegaCity Time and the DN1 RSS feeds.