using supermalloy as the core for wifi loop antenna
There's also the issue of it being a good conductor, which would lead
  to A LOT of hysteresis loss...


No, hysterisis loss is the magnetic material not having a linear BH curve and magnetically saturating when flux density rises too high. If the material is a good conductor then it has high eddy-current losses/problems.

Think about why ferrite is a good for small transformers and inductors - it barely conducts electricity therefore the eddy currents induced in the core are nearly negligible. This is because the particles that make the ferrite are seperated by a non-conducting glue (for want of a better word).

However, as frequency rises eddy currents do become more significant - think of these "particles as exhibiting capacitance to each other then at high frequencies the capacitive reactance is low and the eddy current losses become high again. This is why the frequency versus permeability curve (as shown in my previous answer) has two graphs - one of actual magnetic permeability and one of losses.

Consider an AC transformer - they use laminates and each laminate is insulated from each other by a lacquer - this greatly reduces eddy currents but as the frequency rises, standard AC power transformers become useless - they would need progressively thinner and thinner laminates to avoid the eddy current problems at higher frequencies. This is why ferrite (or powdered iron) is popular for switching power supplies - in effect the "laminates" are microscopic!

Supermalloy has a low resistivity therefore it won't work. The wiki page quotes a resistivity of 6.0 x 10−7 Ω·m and regular iron is 9.71 x 10−8 Ω·m barely 6 times smaller. Here is a table of resistivities for various materials: -



Note that FeNiZn has a resistivity of 1,000,000 Ω·cm compared to Fe which is 10 x 10−6 Ω·cm (sorry for the change in units but basically for Ω·m reduce the of Ω·cm by 100).