Memory with endurance limits - yikes! I'd hate to have to manage that. You would almost have to buy an extra set & validate it just so you wouldn't be faced with lack of supply or compatibility for your particular set when you have to replace it x years down the road.
I think I'd rather have research into 1TB DDR DIMMs than 1TB XPoint NVDIMMs. Let me use 3D XPoint in my SSDs - like bigger & better Optane SSDs. There I'm facing endurance limits already with SSD storage, so it's nothing new there.
The first use will be applications that know how to use the persistent memory space. Think column store or indexes for databases. You won't really worry about endurance because the first uses will be read intensive applications.
Actually 512 GB dimms exist, IBM uses them in their z14 servers, but you're still correct in a way because I'm pretty sure that you cannot use these dimms outside of their machines, so 128 GB would be the largest you could 'buy and use' in a 'typical' machine.