I just looked this up. Instagram currently owns the most relevant live trademark for "INKWELL" [1] (class 009). Apple's registration [2] is indeed dead / cancelled.

You could possibly try to register the "INKWELL" trademark for an RSS reader, since that seems quite differentiated from Instagram's claim, but IANAL, so who knows how successful that process would be.

[1]: https://tmsearch.uspto.gov/search/search-results/86733442

[2]: https://tmsearch.uspto.gov/search/search-results/78126699