A North American trademark (number 85325626, if you want to see it yourself) found by Siliconera suggests that won't be the case. Level-5 filed a trademark for "Professor Layton and the Last Specter." Last year around the same time, Level-5 trademarked Professor Layton and the Unwound Future, which was then announced at E3 and released in September. So it seems likely Nintendo has at least one more game in store for the regular old DS this year!
Now, let's just hope London Life survives localization.