Agreed.
Depends on what your ideal are. ;-)
Usually. What about those full-range ribbons?
IME, a very weak interaction from the speaker terminal side.
So small as to be hard to measure.
Those kinds of heroics are completely unecessary with well-designed speakers. There are very few home audio speakers whose minimum impedance is not well-modeled by a resistor whose value is 3 ohms or more. That's nothing like a short circuit. Power amps that can handle that kind of load comfortably abound.
Almost all room/speaker interactions are confined to the acoustical side.
Speaker cables are generally so linear that even measuring it, let alone hearing it, is close to mission impossible.
If by nonlinear you mean linear effects in the frequency domain, then almost all real world cables are dominated by relatively small amounts of series inductance. A small inductor in series with a 3 ohm or greater resistor (the worst load most speakers present) is a relatively easy load for any competent power amp.
Most of these exotic cables are well-modeled by same equivalent wire gauge twisted pair, on their best days of their lives. Some of them are actually worse than simple twisted pair, but again nothing that should upset a competent power amp.