Trading Wii Points for DSi Points: Not Possible

No. The systems are entirely separate:

• Different Platforms: Wii Shop Channel vs. Nintendo DSi Shop.
• Separate Accounts: Points tied to each console's unique Shop account.
• No Conversion Tool: Nintendo never provided an exchange mechanism.

Wii Points expired with the Wii Shop closure (2019). DSi Shop closed 2017. Both currencies are now defunct.