I can’t find anything on google about what the update includes so I took bits and pieces from Reddit. (Thanks r/animalcrossing !)

• Amiibo functionality, invite characters to park in a special new area. Works with all AC Amiibo, the cards, Splatoon and Zelda Amiibo.

• Wisp appears once you progress to a certain point (unfortunately this is a bit vague)
• Amiibo villagers can be talked to, invited to camp, or invited to live in your town permanently from Wisp
• Wisp can only grant one wish per day

• Amiibo camera that allows you to take photos with villagers

• HHD’s decorating mechanics added once you have the necessary upgrades. Talk to Lottie at Nook’s Homes in order to unlock
• Requires house to have a second floor and new secret storeroom upgrade
• Clothes can now be hung on walls
• Storeroom upgrade provides tons of new storage space 

• MEOW coupons, a new currency from doing tasks. Used for purchasing items at the RV park store and furniture inside RVs.
• MEOW coupons can be exchanged for bells at the ATM at a rate of 3,000 bells per coupon
• Tasks are now displayed on your TPC

• New minigames obtained by having the WiiU/N3DS furniture
• Desert Island Escape
• Puzzle League

• Special items and furniture if you link up save data from HHD  

• Can liquidate your town assets when resetting your town.
• Can choose to either keep catalogue or sell for more bells
• Money can be gained instantly as one giant sum or as 100 daily payments with 10% interest

• Ability to silence people in Club Tortimer

• New island minigames

• Ability to sit on rocks

• New villagers brought back from older AC games

• Free weeding if you haven’t been to your town in a while

• Nintendo 3DS image share can now be used in-game

• Balloons no longer exclusively contain balloon furniture and can now drop any kind of furniture

• You can now shake trees with a net or fishing rod equipped

• New items obtainable through fortune cookies including the Wii U and N3DS furniture

• Your character’s arms will now match the color of your mii mask

• New clothes/accessories ? 

• You can now interact with furniture items while sitting near them

Will update as more information comes out.