This jibes with my understanding as well. I believe that research into mRNA vaccines began somewhere around the very early 1990's or very late 1980's, so the idea itself is not new. And vaccines (or candidate vaccines) were developed for earlier illnesses like MERS, but none ever made it as far as approval for widespread human use, for various reasons. Mostly, AIUI, because the outbreaks ended before they got that far and so it was no longer economically justifiable to continue the process.

So yeah, basically, COVID came along and suddenly there was money and impetus to push the thing over the finish line, and so here we are. That's my lay-person's understanding anyway.