I'll stick to English due to not everyone speaking Polish out on this forum. If need be I can do bilingual posts.
I've looked around some forums - DWS, Odkrywca, some websites, the wiki of course as well. Many hours of digging over the last several days...

Then this site: https://www.commonwealth-triumphant.com has some interesting what if...? vehicles - some were being worked on, some I'm pretty sure are fake.
What I did find was a gold mine of information, I'll share it here. It's image heavy, but rather images than a thousand words each.
This has nothing to do with making a mod for OG at all, absolutely.
I'll go from the stuff that was most realistic to the "there were design discussions in the design bureau", to a few feasible but what I'm convinced fictional.
So first off, the 7 Ton Polish (7TP) tank was up for an upgrade. Some say it already entered service.
Others that it was to be the production run due to enter service in early 1940 was to be the first one of the new type.
It was commonly known as the 9TP due to its increased weight, and per the wiki, one of the early units is the one that doesn't look like the others in this pic:


There was also the 14TP tank in development, which was to be armed with the 37 mm Bofors, but upgunned with a 47 mm gun when the gun became available:

There was a prototype tested of a Christie type tank, the 10 TP, but the wheel+track system was too complicated, so this design was upgraded to tracks only and the prototype for that was never finished before the war.
This is the 10 tonner:

The PzInż 303 scout car had an armored version in the works....


Is it realistic to assume that this car would get an AA MG mount during development? This was getting very popular with Polish designs at this time.
A bit further down the road there was the 25TP tank. 75 mm gun.


This tank apparently had a wooden mockup built, and the mockup along with the documentation was lost. The above is a recreation of what it would have looked like. This was one fun forum topic to read through.
https://forum.odkrywca.pl/topic/323402- ... /#comments
I'll skip the multi-turret tanks that are found in WoT, those I know for a fact were cancelled, and I mean there's already a tank that fits between the Pz IV H and the Sherman 76 just mentioned, so the multi turrets were thrown out for good reason.
Then there is the kind of sort of iffy category. From what I found, these would not be pursued for further development.
Is it realistic to assume that since the chassis was made, and prototypes were tested for a couple years, that this family of vehicles would be approved for production, at least until the better designs are ready? It seems that this family of vehicles was to be just testbeds, because the newer and greater things were to be ready in just a couple of years.
Let's say WW II breaks out, but due to an Obrona Chęstochowy and a Cud nad Wisłą Poland is not conquered, and now needs equipment to deal with Pz II's and BT-5's due yesterday.
There was the family of PzInż 130 (amphib tank), 4TP (scout tank), PzInż 152 (arty tractor) and PzInż 160 shown below:
Now for the "design discussions" category:
PzInż 160 - there was a big move to replace main guns on tanks from the 37 mm Bofors to the 47 mm Pocisk.
If the 160 went into production after all, what are the chances it would get upgunned? It was a good meter longer than the TKS-D, so it should be able to fit the 47.
Further speculation from me - what about the 65 mm mountain gun? There was a push with the TKD and Carden-Loyd to put a field gun on a self propelled chassis, and while the TK series won against the 160 because it was cheap, it was later decided that those tankette gun carriers are too lightly armored.
PzInż 342.

There was a project of this truck to be an AA gun portee. I was not able to find what gun it would carry, I doubt it was a 75 mm.
Anyways, that ground clearance, those tires.

I found similar info about the PzInż 202:

This one was also to be an SP AA gun. I assume a 40 mm? Or could it carry the 75 mm wz 36?
After that there was the PzInż 222, a smaller half track, on which there was an armored version in the design discussion stage:


There was also talk (or so some smart people on the internet wrote), that this vehicle would come in a fire support variant with a twin 20 mm.
The 7TP was also to be developed into an AA tank with a twin FK 20mm gun.
Pure and total speculation zone below.
Now in the end, a few questions.
Did anyone ever run into anything about a tank destroyer on the 14TP?
By "anything" I mean either mentioned by historians, or in the archives or some other reliable source. I'll be happy with just draft notes, memoirs, etc, don't need prototypes. After all, when designing an alternative history, some things will simply not fit with the original timeline anyways.
This would be akin to German E-Series tanks and such. Never fully developed, but with enough info to make an educated guess on their looks and capabilities.
It would be very similar to the Hetzer in size, weight and capabilities if armed with one of the 75 L/50's that were available.

This one uses the wrong chassis (should have 4 road wheels per side, but it still looks cool).
The site also has a 120 mm gun/mortar SPG on the 14TP:

Then there is a cherry on the top that I found on a Russian website:

A 25TP tank destroyer armed with a 90 mm gun wz.39.
Oh yeah - after looking at that tank destroyer I found out that such a 90 mm gun actually totally existed:

So there is at least some grain of truth in the TD drawing....

What about armored gun trucks? I know of Kubuś, but that was a one off.
And finally - what about a 7TP or C7P mount for the 75 mm "Schneider"? Something in the same spirit as the TKD, only bigger and better.
The only SPG I know of was the 75 mm AA gun mounted on a truck chassis, and these were not only shooting air targets:

