Just my two pennies worth:
I really don't see the appeal of the OT and A4 mkIIs. If you already have an OT or A4 there doesn't seem to be anything extra there to justify such a cost. I think if I got a OT or A4 mkII after having the originals I would initially be really excited, then realise after 2 days I've basically got the same machine.
The AR at least has the sampling capabilities added, I could definitely see that as a genuine difference.
And purely subjectively I really am not a fan of the looks of any of the MKIIs. I loved the brushed metal of the MD and MM, and the almost jet of the MK1 OT, AR and A4 / AK. All really beautiful, and all stamped with Elektron uniqueness too.
The new designs just seem too generic to me - they look like they could have been made by any other electronic music company to my eyes.
Edit : also not a fan of the bigger size. Pure Goldilocks - new ones are too big, Digitakt is too small - MD MM and MkIs are just right!