Firstly, many small children have collapsed nail joints, which most tend to grow out of with time. This is different to true hyperflexibility or hypermobility. Taubman always believed that with the former, it was better for the last nail joint to be a little wobbly rather than to pull the nail joint towards the palm in an attempt to correct the problem. In the Taubman world, this is called curling, and creates tension throughout the forearm as well as limiting speed.
Overcoming collapses due to hyperflexibility is all about learning how to stay in the midrange of motion, as someone with hyperflexibility has a greater range of motion than others who do not. This does need to be worked through, as otherwise the person will always feel a sense of insecurity playing with collapsed joints. First of all, I have the student observe that their hand hanging by their side does not show any signs of hyperflexibility, nor when they walk around. The main bridge, main knuckles and nail joint knuckles are all intact. Then, I have the students drop onto the lid, and ask them to observe whether the joint is collapsed or not. You can help them experience what it is like for every knuckle to feel present by supporting the collapsed knuckle with your finger on top and / or underneath the knuckle. Then, have them do the same with their eyes closed. Some may find the visual more helpful, others the kinaesthetic. Once they can identify the difference between a collapse and their finger feeling strong, then they can practice at home and actively participate in the process. You can make a game of it with children, call it “putting on your scientist hat”, or whatever you can think of to make it fun.
This is a process which does take reminding, and it is usually not a five minute fix. However, in my experience it is absolutely possible for a pianist with hyperflexibility to learn to stay in the midrange of motion. When this is learned, there is no reason why they can’t go on to develop at the piano just as well as anyone else.