I use cheap midi keyboard with my A4 mainly to play some melody lines over sequencers playback and for programming sequencer. With A4 I like possibility to take only one small unit without keyboard when it is not needed and easily connect external keyboard when it is needed. Also it can help to save space on desktop.
AK is very nice and I like the concept of it, but it can’t give me this portability.
Also we have the same OS on the both devices and mainly the same functionality except individual outputs. So, with good external midi keyboard it is possible to emulate most of AK features and probably add additional ones.
I racked A4 with OT in 12U SKB rack case and plan to add one more elektron box into it. Also I’m looking for a small portable keys like Korg Microkeys but with midi-out port to put it into rack case to have only one case with all devices which I needed in.