I don’t know of a project that does this, but if I was to tackle it I would convert the RSS to the Activity Streams standard - www.w3.org/TR/activitystreams-core/.

Activity Streams are basically the new RSS and it’s a lot better. You have a separate record for each value in the feed, each one could be stored in a database row or just as a separate file on disk. It also uses JSON instead of XML, which is easier to work with.

Mastodon is built on Activity Streams - so you shouldn’t even need to touch RSS at all. The RSS feed is an alternate version of the stream.