What did you find the most interesting about it?
I don't quite believe he was a Rothschild but the concepts he talked about hold.
The problem of royalty was that they were in the picture when making decisions along with the problem of succession that would stimulate internal strive within the powerful family. A family that is pulling strings in the dark wouldn't have to deal with both of those issues.
Preserving family bloodlines, wealth and knowledge is a primary goal for humans. It would make sense that the ones on the very top are great at doing this. They are aware of this, it's a shame that people in the modern age don't seem to be aware of it. The only extension of yourself if you die is your genetic material, and that can last a very long time.
The poster in the thread doesn't seem to have a nihilistic world view at all. He thinks that continuing and perfectly crafting out (your) bloodline is the main purpose and goal in your life. That is because wealth and knowledge can be transferred through genetics. Therefore it would be the most lasting contribution. He gives a reason that it would be very important thousands of years later for seemingly religious reasons.
It is an interesting perspective and it definitely aligns with human biological goals and why humans behave the way they do. The truth indeed is if you have no religious views that then family progression is the most important. If you simply don't care about that then everything would be meaningless.