Alas, I too fear this is fated to be a very short thread. Ironically the naked bike rides are likely to be low risk- generally participants inevitably remain a metre or two away from each other, the elements quickly disperse any localised contagion, and there are few shared surfaces involved. Advice is that outdoors exercise is even encourageable for those self isolating, for mental and physical health reasons.
But the symbolism of the events are such that when all other gatherings are cancelled, the organisers won't want to risk being accused of reckless behaviour, or worse. Let's hope it doesn't make a permanent dent in future ride participation.
As a minor aside, the Beltane festival in Edinburgh is also cancelled.