I just read a post from a reliable source on the se7ensins forum that said Rockstar are planning to add checks that search for and remove any cars with nitrous from every GTA Online players garage.
'This will be done in the next patch (1.11) via the script.rpf in the update file. They will also be patching the current SP to MP car glitch'
Apparently Rockstar are planning to bring out the nitrous feature as part of a future DLC which will involve pink slip races.
Now I'm not 100% sure if this is information is correct or not but the same guy was spot on about the Rat Loader and Clean Karin Rebel being restricted before the patch was out.