20-Year Prospect
Even though adjusting clothes to their perfect fit has been around forever, it's not as popular a profession as it was just a few short decades ago. People these days are more interested in the quick fix than taking the time to make sure everything fits right, which may be why people don't often wear full suits anymore.
But all has not gone bust; apparently, the big boom market for this career is in hotels (source). With global business exploding in the coming decades, the hotel tailor is expected to take off in a big way.
Imagine staying overnight in Hong Kong and picking up a suit that day for a meeting the next. You're only in town for the evening and you don't have any time—or ability to speak Mandarin—so you're out of luck. That is, until you find out your hotel has its own tailor. That'll be a wonderful day.
Alternatively, you can try your best to create a following for yourself. Job security as an independent in this field will depend on loyal customers who love your style. Keep at it, and maybe someday you'll have a following on Etsy keeping you busy with more work than you can handle.