The official Nintendo website in Japan has upgraded Diddy Kong's render, which could be a hint that a new game in the Donkey Kong series is in development. The most recent Donkey Kong game was Mario vs. Donkey Kong: Tipping Stars for the Wii U, which was released in 2015.
The Donkey Kong franchise has been busy in a number of ways outside of mainline appearances. King K. Rool arrived in Smash Ultimate, following years of fan demand. Mario + Rabbids Kingdom Battle received a Donkey Kong-themed expansion pack, which brought Grant Kirkhope back as a composer. The highly-acclaimed Donkey Kong Country: Tropical Freeze was ported to the Nintendo Switch in 2018, adding Funky Kong as an easy mode in the process; this might be the most recent Donkey Kong game for many fans, considering the low userbase of the Wii U.
It's been a long time since the Donkey Kong series received a new mainline entry, but the return of the DK Crew could be nigh. According to Nintendo Life, a Twitter user named BlueCatBanjo73 noticed that the official render for Diddy Kong had been updated on the Japanese Nintendo website. The render can be found in the Characters section in the Super Mario Bros. part of the site. The previous render came from Mario Party DS, which was released in 2007. The Mario Party DS render was used as recently as Mario Kart Tour.
The most noticeable difference between the two renders of Diddy Kong is the detail in his fur. The Mario Party DS render has fur that almost looks like clothes, with most of the detail being in the wrists and ankles. The new render has much fluffier and more realistic fur. This is more in line with Diddy's appearance in Super Smash Bros. Ultimate. All of the characters with fur (like Donkey Kong and Duck Hunt Duo) had improvements made to the body hair on their character model, especially compared to their appearance in Super Smash Bros. 3DS/Wii U.
It's possible that this new render means that a new Donkey Kong video game announcement is on the way. The Switch's 2021 schedule is looking bare and it would be in character for Nintendo to suddenly announce a new Donkey Kong Country during a mid-year Direct and release it a month later. The render could also mean nothing. It's possible that someone at Nintendo noticed how outdated the Diddy Kong model was and had it replaced to better match his appearances in recent games. The fans are long overdue for a new Donkey Kong game, so any hint of a new entry is bound to make people excited.
Source: BlueCatBanjo73, Nintendo Life, Nintendo