I'm referring to this, which runs for 10 days:
Basically you can trade in your blueprints for:
- prem time
- crew training books
- bia crew members
Although I currently have no use for my blueprints, I suspect that WG probably wants to introduce a new line or something and feels that the proliferation of blueprints has eliminated the grind and this lack of suffering has had some sort of impact on their bottom line. I think the limited time period is to give people fear or missing out if they don't sell.
I currently have over 900 national fragments (including several for fully researched nations) and over 650 universal fragments.