[quote=@ASTA]
>Railguns 

MBT armor plating has probably advanced to the point where conventional cannons are wholly ineffective against it. 

M1A3 is the new T-54/55 of 2050.
[/quote]Railguns aren't THAT much more effective, actually.
Multi-stage cannons and/or liquid propellant can easily make up for the difference.
Heck, even going for 150mm range guns would be cutting close to that level.
Actually, conventional cannons have a lot of advantages over railguns so long we don't get to unrealistic stupid high levels of power.
Mounting railguns would basically limit a tank to be a one-trick pony which uses the same method to engage all kinds of targets.
Meanwhile conventional cannons can use various sensitive/intelligent munitions, gun-launched missiles and actual complex ammunition.
Albeit this versatility comes at the cost of ammo.
Once the rail erosion issue is solved the Railgun is actually a much more economical weapon on the long run. We are 35 years in the future so I suppose the very least people solved this much.

Speaking of which, technically the setting would also support railgun rifles, too.
Railgun components scale down relatively well and your only concern is the power source.
I think compact enough batteries with solar panels and other alternatives for charging are doable.
Personal laers are possible, too. But well, they would be pretty poor in this aspect.
I made calculations assuming a 100kW pulse laser weapon with the spot diameter of 5cm against human targets. It works rather well against unarmored enemies but once I put it against any sorts of body armor material you won't even burn that through a millimeter. So your only chance is hoping the armor wasn't treated to block radiation and the bleedthrough is sufficient to harm whoever is inside that suit.
That's a 100kW system (my anti-missile defense if you wonder, wanted to test how it'd fare in anti-infantry role)
You'd be happy to have a 1-5kW handheld laser rifle with your infantry.

EDIT: But yeah, M1 Abrams or Leopard 2 would be pretty much the T-54/55 of the setting if not worse.
At first I wanted to say T-72 but those tanks at least have the potential to put up a fight.