There was less population density then, and medical capabilities were much more limited, but also less travel (and smaller distances, over greater time)... and it's a different vector. It's a very mixed bag... 1918 should absolutely serve as a stark warning as to what can happen. In truth, this is still the first wave, stretched and dampened somewhat by containment attempts. As weak as some have been. Our best guide right now is Australia... it hasn't been an easy winter, even though they managed the initial outbreak pretty well.

Gut assessment is lethality will generally remain somewhere in the 5% range for several months still, but I expect R values and transmissibility (through both mutation and seasonal factors) to increase first in localized areas of the Northern Hemisphere and then worldwide. The unknown is to what extent first infection primes host for hyperimmunity on second infection. There's no way to know, but it's very possible the second wave of the 1918 flu was so much worse due to that, and not a massive mutation / genotypic shift towards lethality. Hyperimmunity is also a major issue with vaccine candidates.

Immune modulators are the only realistic, long term solution.