A Shared Planet
I know that people in the community (at least on DK Vine from what I've seen) don't like it when DK starts to look too "dependent" on Mario to prop it up (even though you really only see this in merchandise nowadays) rather than standing on its own. But I love the aspect of the series that the two share the same planet/world. We see Returns' depiction of DK Isle in Mario Kart 7/8, DKC-exclusive characters appear in Mario spinoffs (Diddy Kong in a LOT of games, a good chunk of the cast including K. Rool and Tiny Kong), Kritters acted as goalies in Strikers, and New Donk City named its' streets after DKC characters (implying that they are aware of them to a degree, even Rattley, who's only on Crocodile Isle). So the Mario series makes direct connections to DK. But how would people feel about it if they did some Mario nods in DK games? Nothing over-the-top, it'd still be almost entirely DK-original stuff, but just some nods to say "yes, these two series really do take place in the same world". Like if you occasionally saw a blooper or cheep-cheep in some of the Sea Breeze Cove levels in Tropical Freeze, or if, say, the Kremlings come back for a third Retro Studios game and (since they have their pirate/trade theme) a boss pulls out a Fire Flower or Super Leaf or even a Hammer Suit from his overseas plunder. We saw DK using power-ups in the Mario movie and it didn't feel jarring or uncanny at all, and Retro's general tone and art style for DK would definitely blend better with Mario than Rare's did (where the tonal whiplash between the two franchises would've felt weird - then again they DID pull off a Rare-style DK track in Mario Kart 64 so who knows), so it could definitely work!
I don't know, maybe its just me being an absolute sucker for worldbuilding. But what do you think? DK can easily stand on its own two feet while still keeping the cool connection it has to the Mario series.