Blueprints serve very little purpose currently. I think we're agreed on this. I personally enjoy them, as hunting for them and trading for them is like a mini-game, even if it is mandatory. I don't think that justifies their existence and I would prefer they just be removed along with professions, as they both discourage PvP by limiting good equipment to people who have invested a great deal of time into the game. The community for FOnline: Reloaded is already small - it doesn't need to be split further by convoluted mechanics devised by the now-hopefully-defunct want-to-be-game-devs of FOnline: 2238. The special stats afforded to some crafted weapons are nice in that they add some variety to a PvP environment that's very focused on one or two particular weapons at any given time. I would keep that system.
With this personal position established, I'll comment on your suggestion.
I'll assess that your suggestion is, at its core, that limiting the availability of Blueprints would limit the availability of certain weapons. This is only true for craftable weapons. Avengers and rocket launchers may be very easily farmed for, so this change would only make it more difficult for them to be crafted. This would make the special stat system for weapons less used, which would be a shame. If blueprints weren't permanent, there would be a number of different ways to make them and the system surrounding them better, and some options wouldn't necessarily inhibit PvP, or impede on other mechanics.
1. Add a timelimit to the use of a blueprint. Use it, and you have x amount of time where you can craft that weapon. Timer starts upon consumption.
2. Blueprints, upon consumption, have a certain number of uses.
3. Blueprints must be kept in inventory to craft. This circulates blueprints more and encourages PvP. I prefer this and think that this is a good idea. Unfortunately, crafters who have already consumed blueprints do exist. Refunding their blueprints would work but the sheer number of them prevents this from being done manually. A script would need to be written specifically to add the item blueprints back to the inventory of those crafters with them already consumed which, while not really time consuming or difficult (essentially an if statement for every blueprint) it would make implementation a bit more difficult.
4. Blueprints in inventory have a certain number of uses. Like the above, this encourages PvP, but reduces blueprint circulation a bit. I predict that needing blueprints in-inventory will lead to them being frequently lost in unrecoverable encounters, which alone would reduce the circulation more than enough.
More frequent spawns of blueprints would be ideal even with #3. Provided that my prediction is well-founded, #4 would be redundant. Combining them would be ideal, where limited use blueprints would be for more powerful, meant-to-be-rare weapons and armor.
Limited use blueprints for items that are meant to be rare is a nice idea. I'm more interested in Combat Armor MK2, Enclave armor and Brotherhood armor being crafted with those limited use blueprints than I am power armor, though. There's no doubt that the broken economy will permit the wealthy to purchase a great deal of, say, Hardened Power Armor blueprints, and be mostly unbeatable, unless those blueprints would be just as or less available than the armor itself. Combat Armor MK2 is easily farmed (moreso than any other armor, I should note, which should be changed,) Enclave armor is not a huge upgrade from MK2, and Brotherhood armor, while generally the best non-power armor, is not such a huge step up that it would be a significant advantage in PvP, even if it is a good counter to gatling lasers. For weapons, the best would still be available to the wealthy at nearly all times, but this would help balance the economy, so this is fine to me. So long as the main advantage would be weapons like Gatling Lasers with +5% crit chance or something, anyway. Avengers should be a limited use blueprint, too, and maybe rocket launchers. This would certainly help diversify PvP, at least in the future. At implementation, there would be a surge of wealthy factions with a great deal of limited use blueprints but this supply would not last. Factions with a lot of TC would be more wealthy to purchase good equipment and blueprints but not so much that TC would provide such an insurmountable advantage so as to discourage PvP. In fact, it would encourage it, due to a lust for equipment that's currently depressingly and consistently sated.