If a virus kills its host before it has the chance to spread, then it has an evolutionary pressure to evolve into a less harmful variant.
The difficulty with this coronavirus is that it can spread asymptomatically AND it takes up to a week before you notice any symptoms.
That's a problem, this virus has less of an evolutionary pressure to evolve towards a more benign variant. Imagine if it were to kill 100% of its hosts after 10 days, if you don't get a single symptom in the first 5 days while you're still able to transmit it, this virus will have barely any evolutionary pressure to evolve towards a more benign form.
Still, the less a virus kills the more it is able to spread, a virus's ultimate goal is to make as many copies of itself as possible.
There are plenty of viruses that have not gotten more benign over time, HIV for example.
Everything considered, I do personally believe that over the longer term 10-30 years, the disease caused by sars-cov-2 ancestors will be less bad than they are now, taking into account vaccination and our immune systems getting used to this newest virus as well.