It's only just recently becoming even slightly viable. With Blank/OCP and Mental fortress, he gains some margin of error for taking some risks without the worry of Ziz definitely taking immediate interest in it. Those perks don't eliminate the risk entirely, but they do lessen it. Before that, anything outside the workshop basically had her name on it. Though still held back by the unknown threats he has knowledge exist, so he still doesn't just go all out. He also wants to let the world, especially the still volatile city, rest a bit so avoiding anything big. Even then, he is taking steps toward powerful surveillance with his stealth drones already, just to feel out the response to who can even detect his stuff.
His reasons for not doing it are risk management and maybe a bit of morality on invasion of privacy (though he already has powerful scanners, and Survey as mentioned certainly isn't gonna take that as an excuse), not ability. He definitely has the blueprints (and the knowledge base to make them viable) and the materials, and his miniaturization, efficiency, and build speed perks make any constraints on initially being too big less of an issue, especially because version one probably doesn't even need to be planet scale, and can instead be local to his sphere of influence.
The Meta reasons for not doing it are because it either works, goes undetected and does what it's suppose to, and then the story becomes relatively easy mode outside of the Endbringers (that can now be properly tracked and studied) and Zion, and maybe a rare few exceptional powers that can't be handled easily even if you know about them, or are just obscure enough (especially Strangers and Tinkertech) that even Joe's scanners couldn't detect them without being specifically designed to. So the story would enter homestretch with those being the only things really worth dealing with. Especially because putting any effort into making the world a better place and succeeding would eventually draw the Entity's attention anyway, as it disrupts the cycle enough even if the source isn't so easily discovered. Sorta like Cauldron really; they can't really make the world(s) a nicer place even if they wanted to because the entities don't want that and would interfere, risking away even their Hail Mary.
Or it doesn't work. Zion, despite not having any experience with this specific tech base, or applications of 'magic' or souls, psion, w/e else Joe wants to throw at it, does actually have something that detects it and identifies it as something to look into. And hey, as the Warrior Entity, whose literal job and purpose is dealing with out of context problems that disrupt the cycle, I'm not gonna say with confidence he definitely doesn't, or that these hypothetical OoC detectors are either passive enough or too critical to his core directive that they're conveniently on, and that Joe scanning the world in a detectable way despite his best efforts to not be breaks OCP enough for them to work. Then the Story enters endgame because now Joe is on a very short clock and the odds, while not hopeless, are certainly not in his favor. He's definitely not winning a direct confrontation at least.
Where we seem to disagree is that I believe if he accepted the risks and went for it, he has fairly decent odds of success. Equivalency gives the shards a fair chance, but they still have no experience with his specific brand, so it's by no means guaranteed they have an answer, or that that answer is in a position to even be useful. It's not like they have a catch all power that breaks every single possible way of hiding, or detects all possible methods of scanning, even passive ones with little to no emissions, or emissions so minor they blend well into the background radiation of reality. If they somehow do have this catch all, it'd be pretty doubtful that it's energy efficient enough to keep it on all the time, especially given just how many Earths they'd need to watch over (though, I will concede that if it's on anywhere, where Zion is would be the best bet).
If they were that flexible, to already have an answer to things that didn't even exist (not 'magic' itself as they've been retroactively attuned to it, but ways of applying it, ways of applying other tech, physics that didn't apply until now, materials that didn't or couldn't exist, etc) until Joe's passenger started twisting reality to make it so, they wouldn't be hijacking other races for their creativity. If they do, it would be by pure coincidence due to sheer age and exposure to many things and/or brute force stupidity that shouldn't work but does anyway; because shards can be idiot savants like that. So possible, but not guaranteed. Especially because Joe's stealth efforts would be top notch and the shards answer would have to be on that level or coincidentally exploit a vulnerability that Joe didn't know to account for.
That said, I actually don't think the risk is worth it right now with what Joe knows, and that the cost of being wrong is way too high even if the odds are in his favor. Especially because pissing off the Entity isn't the only risk, there's others, like Cauldron, that could make life at least unpleasant if they took exception to him doing it, and unlike the entity they can reasonably put 2 and 2 together even without direct evidence, because really, who else even could? Just that it's a theoretical option that shows how much of the world's problems are already beneath his full potential should he stop holding back and desire to fix them, and there wasn't the risk of a Sword of Damocles descending for doing so.
Either way, it can't be built until the end phase of the story if it would ever be built at all (which it probably would, or something like it, because Survey). So he needs in story excuses not to, at least not yet, because after OCP and Mind fortress, why wouldn't he if he didn't have reason to believe Ziz wasn't the worst thing out there? Especially when he's pretty sure he could kill an endbringer if he had to.