For today, I wanted to leave the level of thinking constantly about software behind. Let's go a few years back. In 2008-2009, with the Wii finally gaining some success with it's first person shooter genre, especially with the games like The Conduit and Call of Duty: Modern Warfare: Reflex the milestones for what Wii controls and customization should be, so many other developers had to follow suit. With games like Red Steel 2 and Call of Duty: Black Ops. Not only do they boast wonderful graphics on the Wii with their engines, but they are also attempting to top High Voltage with The Conduit/Conduit 2 control wise.
I think not enough people own Wii Motion Plus for developers to want to take the gamble on requiring it for their game. :( Good read.
From what I can gather, over 20 million WM+ units have been sold to individual users. This holiday season and Zelda next year (wouldn't doubt it's bundled) will likely increase that figure to near 30 million.
TLDR
Releasing a built-in M+ controller will solve your dilemma(Maybe we'll see some around the holidays?).