Arranger keyboards have their day just like the electronic organs from which they spawned, sales in the USA have always been miniscule compared to the rest of the world, so a drop off won’t really be noticeable.
In Europe, arranger sales are also on the decline, (Just ask any of the dealers) hence a lot of arranger manufactures have left the market, or have released just minor updates to a model and extended replacement of other models. (Usually the TOTL ones)
Asian countries are still fairly balanced.
Eastern countries are still on the rise as when the market was buoyant in the west; it was virtually none existent in the East, so it’s a matter of catch up with new ways (For Eastern players) of doing things.
If you look at what the current generation of music requires, (And even the previous generation) there is virtually nothing in an arranger that has any relevance, so as the later generations die out, so will the arranger just like its forerunner the electronic organ. (Note: there will always be a niche market remaining for it, just like there is for all older types of instruments)

Bill