A positive TCR will affect (lower) the equilibrium point on a VV mod or on a mech, but the equilibrium point should very close regardless of material on a VW mod.Yeah, what rossum said, at some point an equilibrium will be reached in wattage mode, vv mode or on a mech mod. Wires that have a little tcr like ss316 are great for mechs. You get a little boost in power at first and then as the coil heats up the res rises and kind of automatically throttles back the power. Makes for much faster firing without getting too hot with the right build.
The large TCR isn't what makes nickel unusable on a VW, VV, or even a mech mod. The low resistivity is. This requires lower voltages at higher currents than most such mods are capable of.