After just over 12 years in business, the Wii Shop will finally shut down on January 30, 2019. This means you will no longer be able to purchase DLCs or redownload purchased DLCs. If you want to keep your DLCs be sure they are downloaded onto your console or, if you're out of space, an SD card. (This also applies to downloadable software in general-- make sure they're downloaded onto your console or an SD card). If you still have Wii Points, be sure to spend them in a way that you have no left-over Points, as those will just be forfeited. A reminder that JD sells DLCs for 200 (for recycled and alt DLCs on JD4-2015), 250 (JD3), and 300 Points. Even if you don't have any Points left, if you still haven't downloaded Firework, Roar, and Break Free this will be your last chance.
Nintendo will also discontinue the Wii's video-on-demand apps (YouTube, Netflix, etc.) on this date. They have not mentioned the Wii's Internet Browser, but that doesn't really work with modern websites anyway.
If you still would like to transfer data from your Wii to Wii U you will also have to do it by this date. While Nintendo has not stated specifically when this will shut down, I believe this feature heavily relies on the Wii Shop so it would be best to transfer now. Note that the licenses (proof of purchase) for JD2015 DLCs may not transfer over (or at least they didn't for me) so if you have any JD2015 DLCs besides Break Free transfer at your own risk.
Note that Wii on Wii U (aka vWii) still only has 512 MB of memory and cannot access the rest of the Wii U's memory, so an SD card will still be needed for Wii overflow
I have all DLC on JD2 and JD3 on Wii and have backed those up on my SD Card. I have backed up the files where they store them on the SD Card on my Google Drive. I also dumped a copy of my console NAND because they also store DRM license tickets for the DLCs to work.
So I've got nothing to worry about. *deep sigh of relief*
And I have no reason to have the Wii DLC for JD4-2015 because those have no Wii-exclusive DLCs and the Xbox 360, Wii U, and Xbox One (which also have support for DLC) have essentially made the Wii version obsolete for those games as far as the gameplay experience goes.
Also, the in-game shops in the Xbox 360/One and Wii U versions are unavailable due to the shutdown of internet services back in November, however you can still go to Xbox Live Marketplace (Xbox 360)/Microsoft Store (Xbox One)/Nintendo eShop (Wii U) to get DLC. The shops on the Wii version are meanwhile still online despite internet features being shut down in November.
I’ve seen those "red with white lightning strikes" icons before. Luckily, I have all Wii DLCs for JD2 and JD3 and I can get all the others for 4, 2014, and 2015 for my Xbox consoles (both the 360 and One).
Also, on Xbox 360 and Xbox One, you can still get DLCs but you may no longer buy them in-game from the in-game shop. You have to go to the Xbox Marketplace website (or the Microsoft Store if you’re on Xbox One) and get them that way, I’ve been doing that. And it does purchase and download just fine.
Redownloads and purchases have been shut down on the Wii Shop Channel (and I’d assume on JD as well), so you can no longer use existing Wii Points. I just checked. It now only shows titles you’ve already downloaded and you can no longer pay for or download any more titles, or view titles you haven't purchased or downloaded (or have deleted after downloading). It looks somewhat different now.
Of course, the Wii Shop Channel has not closed in the sense of going offline, they mean closed as in closed for downloads and purchases. As Nintendo said in the announcement released in September 2017, the former will happen at a later, unspecified date, so that happening yesterday (as many people out there were probably assuming the announcement meant) is false. Only redownloads, downloads of free content, and purchases with existing Wii Points are disabled. So yes, the Wii Shop Channel (as far as viewing it goes) and its heavily worshiped tune still lives on.