It is a PR stunt because that's what William learned when he was growing up and that is what I have seen him reach for. In no way can someone at their social/wealth rank spend such a night without considerable risk to themselves - and great expense to others - hence it will not really be what a homeless person experiences. No more than William's going to an amusement park when he was young being photographed by a phalanx of photographers - was 'normal'.
Basically, it will be like camping out except on some dirty pavement that's been spat upon and maybe urinated on under a bridge, in a park on a park bench, again where animals have likely done their business - with bodyguards and police around. Kate can just use her imagination. There is far more than addiction and runaways - there are seriously mentally ill people - and the reality is cold, wet, dirty, smelly, hand-to-mouth, day-in-day-out - dealing with hostile police, property owners and everyday pedestrians, not to mention other homeless people that can be dangerous. I am admittedly painting the harshest picture - there is another side to it - which one night on a heating grate will not appraise one of.
Get caught in an airport during some emergency and you'll get the drift of what it's like to not have access to a bed, a toilet, a proper shower, food, water., etc.
It's a political statement if the homeless are allowed on the palace grounds? Interesting idea. The system isn't working - bare bald fact of it. There is no excuse that some of our number are forced out onto the streets to live, to panhandle, to beg. As long as we are in societies whose rationales are based on ownership - we will have the dispossessed - and the conundrum of what to do with them when they no longer are of use to anyone.
The questions are large, indeed, that William - and Kate - are purported to be interested in. If I see him - them - honestly and courageously really studying the issues - maybe attending some post graduate courses in economics, sociology and political theory - really looking at how things work - I might start being impressed with his - their - sincerity. But popping down to the homeless shelter for a photo-op? Nope, doesn't do it.