Compulsory helmets were introduced in the 90s, which was a major advance in rider safety measures. Think about it, prior to that cyclists rode the same decents, the same corners, the same cobbles, with nothing protecting their heads. Beyond this there really isn't much else to do in terms of what a rider can wear to diminish the risk of serious or fatal injury after a fall. I'd have to look at old footage, but it seems to me that road furniture (which has increased over the years) is generally more padded than it was in the past. There was also less policing of sprint finishes to relogate riders for physical contact or moving from a line. Overall there is more awareness about having to take safety seriously in the peloton.
And yet the speeds have increased considerably, the riders seemingly compelled to take big risks to get results or be out of a contract. Sure it was like this in the past, but the sponsorship and management pressure today placed on the riders has probably increased, as larger investments and performance science to eke out every possible advantage have created an environment of hyper-expectations.
So, in short, I honestly don't know what can be done to make a sport safer that is inherently one of the most dangerous by its very nature: ride as fast as you can, shoulder to shoulder, elbow to elbow, on often narrow, twisty roads, under physical and mental duress, with little protective gear on your body.