But if you're doing a complete read-only copy of roam, why not go all the way and make it editable, and compete with them instead?
You could say openness is “a feature, not a product”, and it’s a feature that could be retrofitted.
You could put in a lot of work, just for read-only feature parity.
Or you could work some more, and have a competing product.
You seem adamant, that the former is a better path, but I don't quite see why would you do all that work for naught.
(Roam already broke my backup script 2 times, and there are better uses of my time than interfacing with a proprietary product, if there are better alternatives.)
Do yourself a favor and check if the exports actually have what you need, before blindly trusting it.
I am just pointing out that closed source doesn't necessarily mean 'not in control of your data'.
If it will be my second brain (please note how important this sounds), what I want is to be able to be in full control of the data I generated with it.
I'd happily pay for an Open Source SaaS service from which I can download my data and use it in my own computer/server if I wish to do so, much like Sentry or Strapi.
Edit: Clarity, grammar and spelling