Optional is best, IMO. Now if the Wii had originally come with Wii motion+ right from the start then having a large portion of games require it would be fine. Since it hasn't been there from the start there are at least 50 million controllers out there without WM+ (well above that I'm sure since I'm just counting the 1 remote that comes with each console), so making that mandatory would be ludicrous. Like I said having the option to enable or play the game without WM+ is best for everybody.
Also some games just don't have a need for WM+ support. Just like when the DS first came out, most games tried to incorporate touch screen/wi-fi features just to have them, but for some games that's just not necessary.
starcraft: "I and every PS3 fanboy alive are waiting for Versus more than FFXIII.
Me since the games were revealed, the fanboys since E3." 
Skeeuk: "playstation 3 is the ultimate in gaming acceleration"
