We hired one for a weekend for a wedding and it had a loo and was very useful, especially for dd in the night.
We are looking at buying a van, looking at two in particular, one has a loo, the other one still opens up at the back and is therefore a lot lighter and has more space.
I have never had a campervan before, we've always had tents and used the site facilities but obviously with a van we will be out more and might find we need it. I just don't know how much we'd need it given the space you lose.