I don’t see any real updates coming to the A4 (or the rytm/octatrack), I think they’ve maxed out the hardware. I do love it, even though it’s not as immediate as the newer boxes. The thing that attracts me to the DN2 is the 16 tracks. Great for layering and creating polymeter chords. It’s tough to go wrong with either one and the A4 mk1 can be found used for a very reasonable price right now.
I will say, the more I use the ST, the more I find that it can do. I’m using the analog machines for all of my kick and bass duties now. It’s so easy to dial in and get interesting sounds from. And the Euclidean sequencer is a really great addition too.