The only builds that actually need to break fire/cold immunes are Fire/Cold sorcs and Fire trappers. All the other builds do enough physical damage to be fine.
Buffing Cold sorcs is like the last thing that needs to be done. It and Hammerdin are the most popular builds in D2 already. Fire is a little more hit or miss, but there is nothing stopping a fire sorc from dipping into FO and being fine TBH. As for fire trapper, TBH for them to be viable they’d need to give them the druid treatment and add some physical damage to their traps.
If anything we should be raising the resists on lightning immunes, and adding more magic immunes to balance things better.