Nintendo has confirmed that the demos which gamers can download from the eShop on the Wii U will feature a similar “Play Limit” as seen on the 3DS handheld.
Basically what this means is that you will only be able to play a demo (for example, ‘Rayman Legends’) a certain number of times before it blocks you from playing it at all. If you do attempt to play a demo after you have exceeded the number of plays then you will be asked if you want to go to the eShop to view more information on the product and are then offered the chance to purchase it.
Per demo, the amount of times you can play are different and Nintendo has confirmed that it is up to publishers to decide how many plays a player can have on their demo before it no longer functions correctly. Current demos on the Wii U eShop are Fifa 13 (10 plays), Rayman Legends (3o plays) and Sonic & Sega All Stars Racing: Transformed (15 plays).
No reason was given by the company for imposing these limits.