How many people can you think of who succeeded at more than one profession or skill? Forget about historical figures like Leonardo Da Vinci or any other genius. Most people achieve any form of success or recognition in that one field.
Same goes for picking a business niche. Sure you may look at someone now and see they have a few things they're known for but in almost every case they got known in a single field first.
Then years later they expanded what they were known for.
What is your thing going to be?