That post is 6 months old. The x13sae-f is out and compatible DDR5 ECC is available now, in limited quantities, but not cheap.Why not use the ASRock board that does W680 with DDR4 ECC unreg?
I'm currently more interested in the Asus Pro WS w680-ace IPMI board, but who knows when it will be purchasable in the retail market. I'm going to be doing a build over the holidays though, so if the ASUS or GB are not available, then SM it is.