Let's get past the obvious starter; yes, I actually need more than the 32gb I currently have. I know it's a rare case, but it's my case 
But... am I going to find that if I swap motherboard/cpu in a year or two, now I need ddr5 and there's no more ddr4 options?
My natural inclination is a 2x32gb set, but if it's going in the bin when this motherboard reaches the end of its life, I might just limp along with my current 2x16 plus a new 2x8 or something to tide me over until the big upgrade down the line.

But... am I going to find that if I swap motherboard/cpu in a year or two, now I need ddr5 and there's no more ddr4 options?
My natural inclination is a 2x32gb set, but if it's going in the bin when this motherboard reaches the end of its life, I might just limp along with my current 2x16 plus a new 2x8 or something to tide me over until the big upgrade down the line.