It's hard to say. The schedules for prime routes (such as BCN-STN) are known right out to Saturday 30 March 2024 - 390 days hence - and can already be booked.

The schedules for thinner, less-frequent routes, is never known that much in advance. There's no guarantee even that the route will operate next winter; Ryanair are known to chop and change. They will probably not make a decision on such lower-priority routes for quite some time yet; it really isn't possible to give you a definite date by which this route, if continued, will be added to the schedule.