NS successor will be March or Holiday 2024 imo, the platform is in a unique position where it has a monopoly on one side of the market while competing in another which gives it far more freedom in certain aspects than other prior platforms from any company it's a Gameboy situation only now the platform operates in both markets. It's not even about sales performance alone at this point because by the end of next year the platform will hit 90m and the year after that it crosses 100m easy at which point even if it only started selling amounts of 10-15m a year it's already in sales territory that only the top 5 platfroms have hit the platform's position allows longevity in an unorthodox way.
They're going to play this out similar to the GBA situation only the won't be a DS this time to cut things short it won't be a 12 year gap like the GB to GBA but it will be a fair amount of time to let better tech become viable while the brand is being further cemented.