Normally, trademarks come and go. You're as likely to see a 'mark spawn a full-fledged game as you are to see a company sit on a term or phrase for potential future use. Great Detective Pikachu however, is a bit different as it directly ties to a recent, official video depicting a strange, talking blue Pikachu.
Scant little is known of how the game will actually perform or what Pikachu might be detecting, but it has been revealed that motion capture techniques are being used to properly animate the rodent's facial expressions and speech routines. Whether that sounds adorable or intensely terrifying comes down to your opinion on overly-anthropomorphized Pokémon.
Either way, we aren't likely to know how things play out until Nintendo decides to shed more light on this mystery.