Any faction with an anti-tank rifles or heavy MGs (thinking 13.2/15mm) is going to be killer in towns. They may not be outright tank killers but they're going to be the terror of light tanks and afvs. I'd imagine they'd be highly effective tools for the suppression of tanks and assault guns trying to support pushes as well, especially as these weapons could be easily employed from the cover and concealment of buildings.
I'll be very interested to see if the 2.8 cm sPzB 41 makes it in with the FallschirmJager in game. As well as some of the other less known AT like the Solothurn AT rifles.
The 2.8 sPzB 41 could get through 41-50mm of RHA at 60° at 500m with its tungsten squeezebore round so it's a not so inconsiderable weapon.
I think that [Not Yet Included] Italian divisions will be very interesting in this respect with their use of the Solothurn S18-100/1000 20mm anti-tank rifles (used by Germany and possibly Romania/Hungary as well?) as well as an interesting grab bag of 13.2/20mm HMGs/ACs in infantry mounts.
The Italians when eventually implemented will be very difficult to handle with light and medium forces. With this in mind I can only imagine how trollish Guards troops with Boys (or on the other side PTRS/PTRD) are going to be when nested up in a town.