FRB 190520B - An FRB in a young supernova remnant?

FRB 190520B, a repeating FRB near-twin of FRB 121102, has a dispersion measure excess over the intergalactic and Galactic contributions of about 900 pc cm-3, attributable to its host galaxy or near-source environment. This excess varies on a time-scale of $\sim30$ yr and might be explained by a supernova remnant no more than a few decades old. A magnetic field in equipartition with the remnant's expansion would be $\sim1\, \rm{G}$. I suggest the use of baseband data to measure very large rotation measures.