Related: there's a similar importer I have for screenscraped/copy-paste input from Vanguard
here. Reason: Vanguard ofx does not include certain unsettled transactions (some stock trades, IIRC). When I'm submitting a bunch of transactions, typically while tax-loss-harvesting, I need Beancount to be up to date.
Not that it helps with your Fidelity importer, but just sharing another instance where the ofx importer is insufficient, csv is not an option, and one has to resort to screenscraping.
Speaking about which, for anyone using Fidelity, their ofx support is excellent (for now at least), including
direct downloads.