The Nostalgia rules use the 1974 - 1975 AMA rules as the basis for the event. These rules already have provisions for 1, 2, & 3 line control systems. If someone chooses they could use a "down the wire" electronic throttle and have the benefit of throttle control even with slack lines. 2.4 just makes the task easier, maybe. The classic models are really cramped for space so packaging the radio system, while not necessarily difficult, isn't a given either.
To T. J.'s point, everyone at this year's NATS ran Schnuerle ported engines in Nostalgia and gave up the 20 point engine bonus. The Nelson and other highly tuned modern engines just drive home the point harder. A classic single bypass engine is simply outclassed, even with a 20 point handicap.
Once the line is crossed everything is fair game.
Nostalgia really comes down to the plane and the scoring calculation.
I see no harm with 2.4.