You are gonna live your fate and you are gonna like it!
There are a lot of good reasons Eithan left and Abidan's general approach to worlds under their purview was a big part of it.
You can't easily modify a normal tank or combat vehicle to be an IFV. While mass wise they are the same their volume would be very different. You can carry over engine and say turret but structure and armor layout would need to be remade from the ground up.
You could just slap a ton of fuel on...
It's still 17-20k if you want it to have a proper machinegun as a support vehicle. Basically the same price as a decent cargo truck. Not something everyone can afford. Though you could probably do "one per school".
As a combat vehicle it goes to up to 40k but actually can have some armor.
It's...
It's +8 to hit past extreme range with BT sensors and fire control. Which for AC/20 is something like 4.5 km maximum. You are not going to be hitting anything but structures with that. And even structures wouldn't be easy to hit.
You could make it an F class engine if you build it as support vehicle which would allow you to add a lot of stuff. Though it would be around 400-500k for such a vehicle.
Technically they do exist. It's just a pain in the ass to play a game with a few dozen units on each side with BT level of detail. Though some people do try and MegaMek helps.
But even in real world people try to have support weapons or just something cheaper to do things like this. Maybe...
All of the presented variants have too damn much ammo. How the hell are they going to fire 10 to 20 volleys with 23 top armor? Even with 2 tons of ammo by the time they are gone either all of your enemies would be dead or SRM carrier.
Though the worst offender in this department is probably...