It's not a problem to have a shower pan with a drain toward one end.
Swan makes a 60x32 pan with either a left or right hand drain. Or you can mud set one.
This is all new installation, but... We planned for a bathtub/shower combo, so the underfloor (concrete with hydronic floor heating tubes) plumbing is already in. Is it tough to build a large shower floor that will feed into the normal tub drain location? We don't have to forego the tub, but we'd love to think about it. Any help or links would be greatly appreciated ! Thanks for your time.
Using a tubs drain location for a shower drain is very straight forward. We convert tubs to showers all the time.
You can use a ready made shower pan, build a custom shower with a linear shower drain or use a regular drain.
Have you thought about what kind of tile you want?