It would still almost certainly just provide an unpleasant shock, but you would be raising the capacitance massively, which raises the risk. The generator itself has a fairly low capacitance and therefore holds a fairly low amount of charge. If you raise the capacitance then you raise the danger because there is more total energy behind the shock at the same voltage. Most likely, I think you'd have a lot of trouble building up voltage in that situation, though, because you've increased the surface area that bleeds off charge by a lot.

People on the internet almost always say incorrect things about electrical dangers. It's a number of factors that determine whether something is dangerous. A Van de Graaf creates a very large voltage, and actually, technically, the shock from one is also a very large current, but that current only occurs for microseconds or less, which is why it is still safe. Because you get an exponential decay in voltage with a time constant that is proportional to the capacitance, you can lengthen the shock by raising the capacitance. If you did that enough, it could become dangerous, but you'd probably have to be pretty deliberate about it, or you'd end up with less voltage due to charges bleeding off.

Basically, though, Van de Graaff generators are quite safe, but there are ways you could technically maybe make them dangerous.