Nintendo has recently announced on their Japanese website that they are planning to close the Wii Shop Channel on 31st of January 2019. After that date, it will be impossible to purchase titles for both the Wii and Wii U consoles. However, users have only up till March 2018 to top up points into their accounts. Points unused after January 2019 will also be refunded to users.
Those that already bought titles from the store will still be able to re-download their content and transfer it between Wii and Wii U through the Wii System Transfer even after the shop closes down. However, said functions will also close down in the future.
This can be seen by Nintendo showing they are fully committed to their Switch and 3DS console line up as the sales brought in by Wii and Wii U was never as impressive as the other two.