Wii DVD Support
Wii DVD Support refers to the many iterations of DVD-Video support present in early and unreleased versions of the Wii and its software, which were all ultimately scrapped.
Wii + DVD
Wii + DVD is an unofficial name for a proposed revision of the Wii which would have included DVD playback capabilities, which was announced in late 2006 for a 2007 release but was never released.
Reportedly, the system was being developed in a partnership with Sonic Solutions, which later became Roxio (known for making the program "Toast"); it was to use the Sonic Solutions "Sonic CinePlayer CE DVD Navigator" software for DVD playback, and was scheduled for a Japanese launch in the latter half of 2007. No other details are known about this system.
Hidden Software Features
The standard Wii console supported DVD playback prior to release, with DVD video support in a console's TMD being implemented in IOS4.0.1 and at one point was to support DVD playback via an attachment. The Wii System Menu features graphics (and, in 1.0, text) related to the DVD feature; it is unknown when it was cut from the standard release of the system, or if these assets were meant for this enhanced model.
The "DVD" entry in setting.txt, which is always set to 0, was likely used to specify if a Wii console supported DVD playback or not. Changing this entry on final versions of the System Menu has no effect. The "MPCH" setting.txt entry may also be related to DVD playback, as it is set to a fixed value on all Wiis and does not seem to be used. It may stand for "Movie Player Channel", and have been a flag to determine if this channel was installed on the console depending on if it had DVD support or not.
The DVD library function DVDLowEnableDvdVideo(), which calls IOS syscall 50, enables DVD video mode. This was abused by early Wii backup loaders to gain raw access to inserted discs, used to play pirated games from DVDs. The function DVDLowReadDvdCopyright() may also be related to DVD-Video support.
There is a Macrovision test present in RVL_DIAG, which is likely related to the implementation of Macrovision copy protection for the DVD playback feature.
The common definitions file in the Revolution SDK (simply named "commondefs" and present at the root of the build directory), includes a list of internal and external system libraries, including one named "dvdvideo" listed as an external library. Presumably, this would have been used to support DVD-Video playback; since it is an external library, it is possible that third-party developers may have been originally allowed to harness this functionality somehow.