As already noted, Macronix provide the 3DS cart ROMs (specifically their XtraROM with custom DRM). Given that they note "Key customer is planning new generation platform" on the slide relating to their ROM business, we can basically take it as confirmation of three things:
1. The handheld will release this year
2. The handheld exists under the NX codename
3. The handheld uses game cards
The first was already reported, but this is basically extra confirmation on top of that. The second isn't necessarily a big deal, but further indicates that NX refers to both a handheld and a home console. The third one may seem obvious, but it rules out a download-only platform, which is worth noting.
Macronix also product NAND flash, although as far as I'm aware Nintendo haven't used this, and have instead opted for Samsung to provide the flash memory for both the Wii U and n3DS, so they would be the presumptive main supplier (although they may mix-and-match, as they use the eMMC standard).
The DSP used in the Gamecube and Wii was designed by Macronix. It's possible that a derivative of it may have been used in the Wii U, although the IP for it may be outright owned by Nintendo at this stage (Macronix don't seem to have designed DSPs for a long time).
Macronix may provide some other minor components in the 3DS or Wii U, but I haven't been able to find any in teardowns. There's a small EEPROM chip on the Wii U MCM next to the CPU and GPU dies, so they may be the supplier for that.