The guys at Yacht Club Games announced in their blog that the Shovel Knight: Treasure Trove expansions won’t be released in April. Instead, King of Cards and Showdown, the two new games that will be part of the collection, will be delayed by “several months”.
The main reasons for the delays are due to working on both King of Cards and Showdown simultaneously, platform tuning, localisation, and testing.

They’ve also said that there shouldn’t be any further delays after this one but the Shovel Knight amiibo won’t be released until then, either, as they’re going to be part of the new additions.
Yacht Club Games stated that updates will be regularly provided on their Facebook, Twitter, and site.