Same as every other weapon. It has nothing to do with the current method of acquiring FP or +8% versions of those items, even though it should probably change as well at some point.
I want to be able to use a +1% version of my MKII shotty in my pen training build, that's all. If pen versions of MKII weapons were sold same as any other weapon, it would also mean some of them could be allowed in s5 rooms if the community decides that they're not harmful.
The issue I guess is that less people are going to have to craft those weapons purely out of curiosity, since they'll have the option to try out the product they're investing into.
(Currently: "I know people say MKII Light machine gun is bad, but it can't be that bad come on, I'm going to try it out." 2 minutes later: REGRETS)
But then again, many people nowadays do not dare touch a weapon that doesn't have FP stats since they think Fp weapons are ten times better than their pen counterpart so it's still going to be the same, mainly.
Anyway, it's just something to consider.