No, I haven't. Mads reached out to if I'd be interested in reviewing them, and I said I would, but he's busy fulling actual orders right now, and I wouldn't be able to review them until probably 4-6 months from now, regardless, as I have one review I'm completing, and another one lined up after that. So, it likely wouldn't be until the fall that I'd be free to review them. Knowing how well Buchardt designs their speaker and also the high-quality of compnents and parts they use for the crossover, wiring, etc., I'm confident they're pretty wonderful.
As for myself with respect to upgrading to the E50s, I don't have any plans to; I absolutely love my S400IIs. Very happy with them and from my perspective, I'm "done" with respect to system componentry. If I were to put any more money into my system, it would be to purchase additional Shunyata Sigma-X CGC ground cables to connect more of my components with Sigma-X CGC's to my Shunyata Altaira set-up.
Cheers.