One of the first "promises" (agility) of mRNA turned out to be a bit of a mirage.
We have this wonderfully adaptable mRNA vaccine technology - but we've backed ourselves into a corner re: COVID-19 because it seems "original antigenic sin" is a stubbornly real effect in this context. All current research points to updated vaccines inducing largely the same old immune response - they are not more effective than just dosing again with the original shot.
So we can "reprogam" the vaccine but getting the immune system to do something different turns out to be more difficult.
Where it get interesting at a population level is that nearly everybody now has these antibodies for the original spike. At a population level this seems less robust than natural immunity[1], which would have induced (again at the population level) a broader range of immune responses from sites all over the virus. You also would have had a population where some people were exposed to original, some to delta, some to omicron etc, again leading to greater antibody diversity.
In general, monocultures tend to be less resilient to "exponential attacks" than more diverse systems.
While public health authorities have repeatedly dismissed this concern, I still find it hard to believe this kind of "antibody monoculture" isn't going to have an effect on subsequent evolution of the virus.
Mass vaccination was almost certainly the right call from an immediate public health perspective but I can't help but feel it's also left us more vulnerable in some difficult-to-predict way for the long term.
[1] Agree, it's bad terminology but everyone understands it. It's all "natural" immunity, of course.