I'm aware that most of you will probably think that the idea of even attempting this is ridiculous, but No the idea is not ridiculous but need to me looked with right logic. Only conceivable reasons to do this:
1) Avoid theft: would not work - Any normal thief given an opportunity would not be repulsed stealing an unmarked big camera with big glass
2) Avoid attention: Would do the opposite - How many people look at photographer and scramble to read the model # on their camera. Most like the few who frequent forums like this. And even an unmarked rebel would raise the attention level of this group to moon.
3) Style and statement: There can be no arguments against this one. Except, be careful not to damage $3K camera!!!
So far nobody mentioned a real serious reason for "debranding a product":
LEGAL. Anywhere in certain "spaces", which can be TVs, movies, sports stadiums, there can be a legal restriction for professional photographers, vendors etc. to show their brand, if an exclusive right to use advertising space, branding etc. has been given to a specific company. I.e. of Canon sponsors an event, they may not wish to have Nikon shooters prominently displayed during TV broadcasts. So, perhaps Canon gives all the photographers free cameras, but professional XX wishes to keep using his/her Nikon, so it's best somehow to hide that he/she is using a Nikon, otherwise there may be consequences.
Probably quite a number of readers here are aware of the ridiculous limitations that were imposed on shops around the London Olympic venues based on sponsor pressure.
Or the ambush marketing of a Dutch brewery during the World Cup. http://www.bbc.co.uk/news/10321668
I have seen a number of debranded cameras in Tv shows, most likely because of branding/legal issues.
Then of course there are the funny instances where commercials for a MS product are made with Apple hardware, the Nokia PureView ad (http://www.theverge.com/2012/9/5/3295316/nokia-apology-lumia-pureview-ad
So, there are good reasons when you want to hide a product brand.
PS: I forgot the story of the athlete who had a contract with some sports company, but used running shoes from the competition, and added some stripes to hide the fact....