Magic is wonky, upgrade system, blah, blah, etc.
So, the upgrade system was easy to build. Items have a limit to how much they can be enchanted, +10 is the max. Each enhancement bonus and ability has a point modifier, +1 enhancement is +1 and brilliant energy is like +4 for instance. Most of those abilities are easy to hand wave into technology, shocking and shocking burst are now alternating current and direct current batteries that can be installed onto your swords, flaming is now channels built into your blade that can be filled with oil and lit on fire by a striker in the crossguard of the weapon. Armor that conveys electricity resistance is now armor built with thick rubber lining instead of padding. Obviously, it is hard to find a fit for stuff like vorpal and brilliant energy (though I have ideas for that one), but I believe that I have the basics covered.
Basically, what I am saying is that weapons and armor are easy. The upgrades are slightly more limited than magical enhancement, most weapons can only have 4-8 points of upgrade, rather than the 10 of magic items, but upgrades do not require craft magic item feats to use, just ranks in craft skills to build them yourself, or marks to buy them. Being able to build them yourself makes them considerably cheaper than magic items as well, while the general industrialization of Hekinoe makes them far more accessible than magic items are in a typical campaign.
So the problem is that there is no equivalent system for wondrous items or rings and the like. Some things, like the Ring of Shocking Grasp or Gauntlets of Ogre Power (neither of which actually exist in Pathfinder) are easy. Basically a taser and steam driven locking gauntlet set up that attaches to a suit of medium or heavy armor and grants a strength bonus to one arm. Others, like the Amulet of Natural Armor or Cloak of Resistance or Bracers of Armor.
Back in the day (a 2nd Edition AD&D Wednesday), I had this pretty slick cyborg/biomod system based off of Deus Ex for a campaign we were playing that was more or less low magic. But that feels mostly ridiculous, which is not to say there aren't already some clockwork steampunk cyborgs already running around. Anyway, I just don't feel like a system of augmentations really fits with Hekinoe. Perhaps next campaign, when they're robots built by A'lst to go back in time and save Kusseth.
One thought I've had in the past for this wondrous item issue is trying to make it like snake oil salesman style stuff. I tried it back when we were still using 4th Edition, but everyone was kind of like, whatever, and didn't seem to interested. My thought was that you buy Johnson and Steven's Ultimate Homeopathic Lifetime Supply of High Octane Ultravitamins to Energize and Revitalize Your Levels of Vim and Vigor! and gain a bonus on all your saving throws sort of in lieu of a Cloak of Resistance. The problem there is that you have a cloak spot item taken up by a daily vitamin and you get players that freak out because they can't wear a magic cloak while chowing down on their vitamins. Also, writing nonsense like the titles for all of these snake oil elixirs, salves, and so on could get exhausting.
I guess my final thought/ruling on the matter is that stuff that is easy to convert like the Belt of Giant's Strength or the Cloak of Elvenkind, will get converted. Oddball stuff like Belt of Constitution, Crown of Blasting, and Horn of Valhalla will remain as is. If you want it, buy it and deal with the consequences of playing with sorcery. There is a reason sorcery is feared and reviled and fined extensively.
Or you could go buy some psionic items.