Nothing I'm aware of. You've got a couple issues to contend with, first being that GPX is based on XML. You've got a choice to make, convert it to GeoJSON or leave it in it's native format. Embedding data with a schema (XML) or specification (JSON) into a nostr message still has it's own set of issues as embedding JSON or XML within another JSON structure increases the complexity of validation.
nostr:npub1u656f7znujcagfhtgngvtkcflhzptnj38enyzx85da0lh63sfj7qva332p have you seen anyone working on mapping via nostr like this? I know there was discussion about geojson objects, but have formats like .gpx been discussed?
Discussion
It’s like, you can do it, but you shouldn’t do it, however there’s not another option based on existing standards.