The Saudis announced six megaprojects in 2005. King Abdullah Economic City was the only one that went anywhere. I believe it was supposed to have 2 million people and reached about 7 thousand.
They've kicked people out of the area, killed at least one person, trashed the area with initial construction efforts (I've driven past) and now the inevitable seems to be coming to pass already.
They still have time but they need to do something to diversify from oil in the way Dubai has eventually. Building a new Dubai, with a different legal framework (only rumoured for Neom AFAIK), doesn't seem like the worst idea to me, but starting with an overly ambitious design probably isn't the way to get traction. The Middle East do love a pissing contest though so starting small isn't what they're into.