This is sounding dangerously close to the Victorian argument that women shouldn't play sport at all because of their delicate constitutions.
The progress of sports science means that all athletes, male and female, can do things now that would have been a higher risk of injury 50 years ago. Training, technique and equipment all mitigate that.
I agree that female-centred sports science has a long way to go - the impact of the menstrual cycle and the frequency of ACL injuries are the most obvious under-studied areas. But it's simply not true that female tennis players are at a greater risk of injury than male ones, and the "shorter limbs => more injuries" theory doesn't hold up at all in tennis.
FWIW absolutely no one in tennis thinks that women wouldn't be able to handle five sets physically. If they had to play best of 5, they would adapt their training accordingly. Some women frequently play three-setters that rival five-setters in length (don't forget that most women get fewer "free points" off their serves so have to expend more effort in more rallies).
Whether women play best of 5 in the future, or whether best of 5 will be eradicated for the men, is something that will be decided by TV studios, and the latter is far more likely at this point.
I once got to play a five-set match, thoroughly enjoyed it. Would play that format more but committing to that length of time, and having that sort of indefinite access to courts, is rare!