Virtually all arranger keyboards are software based these days, however they are bespoke to the manufacture and they only fit hardware that allows small updates before the complete arranger has to be replaced. (Most also don’t allow 3rd party support)

Only two manufactures (That I am aware of) has long term upgrades, (Some free, some cost) these being Wersi and Bohm who make single keyboard versions of their organs with arranger features included, however the arranger features on-board are designed for organ play, (Where the player plays virtually everything themselves) not arranger play, (Although they do now allow 3rd party (From the big arranger manufactures) styles to be used so as to allow an easier transition from arranger play to organ play for those wishing to expand) Wersi (And Bohm with the optional Cloud Station) also allows 3rd party support via a VST Host on-board so that you can have pretty much anything you want.

Both are niche products, and being hand built cost significantly more that an easy play arranger keyboard that is mass produced, (Also organs have never been cheap) however that no one else has followed suit just shows how difficult it is to bring to widespread market, (Most arranger players prefer to press a button and have everything done for them rather than make themselves stand like the old organ players did by developing their own style of playing (Hence arrangers have always been aimed at home players) even though long term it works out cheaper for the customer and manufacture, (Software is much cheaper to change than hardware) for example the original Wersi OAS instruments came out in 2000 and were not discontinued until 2014 (And this was only because certain 3rd party hardware was no longer available) with many sound and feature updates over this time.

Arranger keyboard sales are on the slide and like the entertainment organs that they spawned from, will become a niche market in the future, but will still be around just like organs are.

Bill