You're talking about tabletop terms, I'm talking about in-universe reasons. In-universe, it takes money to develop a new vehicle, and a Gauss Rifle isn't a drop-in replacement for an Autocannon for at the very least two reasons: power consumption and recoil management.
In-universe, it might cost money to develope a Hetzer variant with a Gauss rifle, but given the existence of multiple variants of the Hetzer that change its layout quite significantly, including a version with a large laser, one with LRMs, one version with SRMs, a version with an LB-X 20 with a fusion engine, a completely sealed version with a fusion engine, I would say it's quite evidently false to say there is no in-universe incentive to develope and produce variants and developement costs don't seem to be much of an issue either, given that exchanging an ICE with a fusion engine or sealing the entire vehicle are quite radical changes too.
Given that there is a laser version, power consumption should not be an issue and the Regulator and Alacorn seem to handle the recoil of Gauss Rifles just fine (the former being only 5 tons heavier, riding on a rubber skirt and having the gun at a comparatively high point inside a turret, I would say that the Hetzer is going to handle it just fine.
If we're going by your argument, there's no reason why we couldn't replace the Gauss Rifle on a Hollander with a bunch of machineguns and call it a Piranha.
1) Why would this be a problem?
2) Why does this matter?
If you want something that can reach out and touch someone, get a few LRM carriers. If you want something cheap to annoy people in urban combat, get Hetzers. Or Urbies, for that matter.
And if you want to get a cheap self-propelled direct-fire tank destroyer, you get a Gauss Hetzer™... especially since you can field almost an entire lance of them for the money a single LRM-Carrier would cost you. It really depends on the niche you need to fill and I never said the Hetzer would a be-all-end-all weapon system for all circumstances, I always said it would be limited to its niche (but I still maintain: that niche is far less restricted than the "If there's no city, I'm in some deep shitty" AC20 version).
And just for shits n giggles: The cost of a Gauss Rifle and an LRM20 are pretty similar, but LRM ammo is more expensive than Gauss ammo (at less savlos per ton, even), so in terms of upkeep and cost efficiency alone, the Gauss wins again.
See, if you think the idea is silly and you don't like it, I am totally fine with that, but you came up with reasons why it wouldn't work in principle and as far as I'm concerned, all these arguments have been disproven both by lore and by rules:
- The Gauss isn't more expensive than the AC20 so that argument imploded.
- The Gauss is rare, but then there's a version that uses an LB-X, which is even more rare (and significantly more expensive, which again disproves the argument above).
- Obviously, Quikscell (or whoever's putting out these Hetzer variants) doesn't mind pouring money into developement, when you look at the wide variety of different loadouts, that change the entire propulsion system, replace the armament with completely different types of weapons or turns the entire thing into a hermetically sealed vehicle.
- Given the price of the LB-X and especially the sealed version, it's evidently false to say that the Hetzer is entirely defined by its low pricetag.
- There is nothing to support the statement that the Hetzer can't deal with the recoil (low centre of mass plus a casemate structure would make it insanely easy to mitigate btw). Even assuming it would demand money and time to develope something to absorb the shock, given the many stock variants that also took time and money to be made, that hurdle would surely not hold back anyone... and just for the record: the 30 ton Yellow Jacket seems to handle a Gauss rifle just fine and the 30 ton Karnov can fire a Thumper Artillery Piece without issue, too.
- Given the number of vehicles and planes using a Gauss rifle, I would assume Gauss-rifle shock absorbtion methods are a well-researched field and a plethora of solutions are ready to use off the shelf - you simply do not have to reinvent the wheel every time you make a new car.
Regarding that last point:

Oil-filled cylinders with powerful springs to dampen the shock of firing isn't really advanced space magic, you know.
A better argument would be that the AC10 version offers almost the same damage at only slightly less range with significantly more ammo and a small edge in armor.
But that's not an argument you made and even if you did, I would still point out that having a greater range (especially in a game that penalizes shots at long range so harshly) and a tiny edge in damage is a sufficient advantage to justify a Gauss version for the financially well-endowed warlord connaisseur. The AC10 version would still be the most cost efficient version for the warlord on a budget, but a small increase in price would allow you to field a very cheap, reasonably armored and mobile platform, that carries the most powerful long range direct-fire gun in the game to round out your arsenal.
But as a bit of a personal takeaway: I bought Hetzer minis a while ago but I could never really decide whether I want the AC20 version or something different but this back and forth made one thing clear to me, the best version for me is the
standard AC10 version. 50 tounds at a reasonable range without a minimum range and a bit of additional armor is a pretty good deal. I dislike custom variants and try to avoid them wherever I can.
Either way, this is pointless. Saying "we need a Gauss Hetzer" doesn't do anything, none of our wishes are canon
I never said I want the Gauss Hetzer to be canon and this entire statement feels like a cop-out argument to me.
Also, a Gauss Hetzer is just a Jagdpanzer IV (70), change my mind.
You say that like it's a bad thing. I'm more of a Jagdpanther type myself...
That thing just looks like it means business.