Power head compatibility

I know the EGO power head is not compatible with the "standard" square shaft used by several other brands.

It seems almost every brand uses that square shaft, but I think there are maybe a couple that don't. Does anyone know if any of those happen to fit with the EGO unit?

I'm thinking of Honda's gas powerhead specifically. I believe Chervon is making Honda's new European line of battery powered tools, right? So there's already some cross-licensing or sharing of products between these brands. Maybe their attachments would fit on the EGO? It looks like they use a splined shaft, but from what I've seen can't really tell if the number of splines or size matches.

I've also seen a brand called EcoPro that might have a splined shaft, anyone know anything about that?

I'd really prefer to buy Ego attachments since I've been impressed with their other tools so far, but with the availability issues, and attachments like the hedge trimmer that are not even offered yet, this could help fill some gaps.