First off, i think bringing this in this way is great, resetting tech skill is something i personally didnt like with the current version of hs.
One thing, and it may just be the way i read it, that i am not sure i like would be if we were to have it so that the class of the player fabbing the item determines the +skill. If it is the class of the person equipping the item, that would be alright, but limiting someone to fabbing for one class would be a bit of a pain.
Having seen the direction that items have gone in HSR, most notably the weapons that were introduced, I think that having a fabbing system to follow along with that would be great, maybe having the fabbed items being a slight upgrade to those dropped by mobs, as an incentive to make them instead of just waiting for one to drop while you grind out a few levels in a system.
Balance is definitely going to be key though, but, one thing that should be considered is something i have seen in many other games, certain fabbable items that use way more mats, and harder to find mats, but the item they make are much better, for your level, than something similar that would be easy to farm, or for that matter, what the market will be flooded with as people fab to level their skill. Again, this is an incentive to fab while leveling.
What i personally think might be an idea is to avoid the idea of the level 75 who is just bored and raises fab, and try to make the items more useful, so that as we get new players, or if you make alts, you fab the items for them so they are better as they go. One way to do this would be to change the way complexity works, and instead of having diminishing returns on the item stats when you are too low a level (or tons of jamming, in the case of weapons) just to make them unequippable before the cpx level. This would require those leveling, and tiering, to have and use the other gear as they level, instead of them just taking up locker space or being DD'd. With the current system, most people, especially when they tier, just use high level systems because the diminishing returns arent actually that bad, and they dont have to worry about changing gear, just weapons.
I realize that many people might not like that last idea because it would require more work and gearsets for tiering especially. I share that sentiment, to a degree, because I can be lazy sometimes and its just easier to have 1 set of gear i use from level 1 to bossing at 75. But on the other hand, if we want to make systems below level 75 useful, especially if we are going to put the work in to implement a great fabbing system, and possibly more planets and bosses (possibly at lower levels, like i have heard Tearix and the asteroids being talked about) then i think the items that drop off of these should be useful. No one uses the Tyv brain, or items like that, because if they tiered, they have better, and if they are new, people will give them better. If that was the best item for 5-10 levels, stuff like that would get used, and i feel the fabbed items could be the same way. Not all of them, some will be generic items with OK stats and relatively easy to farm mats, but some should be better items, with harder to farm mats, that people will use if they dont have the option to keep their umbrals or whatnot on when they tier.
sorry for the longwinded reply, just trying to toss some ideas out there and give a complete idea of what i think.
On another note, I am willing to help with implementing whatever you decide, and whatever else you need. Let me know if you would like my help, probably reply here since the time difference for us means i dont get on often when you are on, and we can go through other means to figure out what you would want me to do.