I work in this field and this is a great summary of mRNA and its therapeutic usage. The article does mention it, but mRNA is going to be widely used beyond vaccines as well.

As an example, at a previous company I worked at that had a robust pipeline and a portfolio of antibodies on the market, they were actively developing an mRNA-LNP version of all of their mAb programs. The idea is that if you develop an LNP platform that can reproducibly transfect say, the liver, then you can just turn the liver into a protein factory for anything you provide the mRNA sequence for. Having mAbs produced and excreted in the body solves one of the big challenges to convenient biologics dosing, bioavailability. Basically, a lot of antibodies, when injected under the skin, have trouble making it from the injection site to your bloodstream. This can be solved by administering via IV, but that has many downsides when it comes to patient convenience.

The reason vaccines are the first successful application of this technology is because they only require very small doses to be effective. Compare the amount of protein that is in a flu shot (60 micrograms in Fluzone at most) to a typical mAb (~150 mg up to 1 g at most), you can see how much less the vaccine requires. I fully expect that as the upstream and downstream processes for LNP manufacture improve and are able to scale, that we will see mRNA take over what is currently the realm of biologics.