Cuphead made quite a splash in its brief debut in one of Microsoft's E3 sizzle trailers back in 2014. Now, four whole years later, it might be to make another appearance at the popular trade show. Funko, makers of those pop culture dolls, might have hinted at a Cuphead E3 appearance at this year's show through a mystery shirt listing.
On their E3 exclusives page, there is a listing for a Cuphead-themed mystery shirt but the design won't be revealed until June 11th. That is the Monday of E3 and the day of Sony's press conference and the day after Microsoft's. Given the timing, it could be revealed to coincide with an E3 announcement. Developer StudioMDHR has not commented on any possible appearance at the show, but Maja Moldenhauer, the game's artist and producer, will be at E3 for an interactive workshop.
However, StudioMDHR has stated that Cuphead will be getting more content. On Xbox's official livestream for the Xbox One X launch in November, Moldenhauer announced that more Cuphead was coming, but didn't say when. She couldn't say much, but said that solo players will soon be able to play as Mugman along with a "few other things up [their] sleeves."
Given Moldenhauer's statement and this listing, it's probable that Cuphead will get some new content and a possible expansion with more bosses and levels soon. The game was received well and sold over two million copies in just three months, making it a ripe game to return to and add more content. Nothing has been announced, but, given how much Microsoft helped with the game, it's likely that this new content would be on their stage if this hint ends up materializing.
Despite the shirt reveal being on the same day, it is unlikely that this alleged Cuphead E3 announcement will happen on Sony's stage given the developer's prior comments. On NeoGaf, Cuphead's developers answered "yes" when answering a question about the game being a lifetime PC and Xbox One exclusive. The developer also stated multiple times that a Mac version is probably on the way along a possible Linux version.