For significant new characters introduced to the IP in other games or mediums we'll be assessing on a case by case basis whether it makes sense to bring them to LoL or not. We did look seriously at bringing Silco over to LoL for example during the development of season 1 of Arcane. We thought he was a great character in some respects (personality, voice, backstory, connection to other characters etc). Didn't make sense for a MOBA however, just the wrong sort of expression of power for the gameplay we offer. Could have forced something to do it, but wouldn't have felt true enough to his character.
For other characters then, like Jack, Norra, others from Arcane, others from future games we'll do the same sort of assessment, plus a comparison to other options we're already considering (e.g. do we think we'll deliver best by adapting a character from LoR or by making something new with a different focus?)