Bethesda seems to have registered the title Fallout: Shadow of Boston at German Patent and Trademark Office. According to the listing, it's supposed to be used for Computer game discs; Downloadable computer game programs; Computer games programmes downloaded via the internet; Auditioning for tv game shows"
That means it does looks like Bethesda is preparing the announcement of the next installment in the Fallout series. Perhaps something we'll see in December if VGX does get another shoot at Spike TV after last year's fiasco. Of course, you may remember rumours dating back to last December pointing to a Boston setting.
Thanks VG247.
Update: The filing turned out to be a hoax as confirmed by Bethesda.