I am sure many would love 88 keys, but that has to be balanced against cost and portability. I think one of things that is interesting is that arrangers grew out of the home organ market but as time has passed they are becoming more 'piano' like with touch sensitivity, weighted keys and extended keybeds. Then from the other end we had electronic pianos coming from the piano market, but as time has passed they are adding more and more synth and accompaniment features. There is still a bit of separation, but that separation may disappear. In some ways other than it is not portable the CVPs are almost already there, although the piano simulation is still a bit lacking compared to the real thing. The future top of the line models we see will continue that merging and integration of functions and be more like a portable version of the CVP. Quality piano simulation is already there, but very expensive, and the models tend to be heavy. But over time the piano simulation will improve and get lower in cost and one day we will see keyboards which match the best grand pianos in playability and sound, have all of the advanced accompaniment and voices of the best arrangers and synths, and are affordable.
Mike