It's a bit complicated ;-)
There are two different soulbound sets:
- The Chaos Legion Soulbound Set
- The Rebllion Soulbound Set
The Chaos Legion Soulbound Set already increased in price twice or thrice (not sure there) and will keep increasing in price until it hits 20x, after that it won't be possible to unbind it ever again.
The Rebellion Soulbound Set is the one I'm working on in the screenshot. It's 20x to unbind right now and will stay at that value until it goes out of print (so probably another ~9 months) at that point the unbind cost will go down to 10x and start increasing again the same as the Chaos Legion Soulbound Set does right now.