Like others I am sceptical this will ever happen. But I'm a bit more optimistic than I am say about London Resort.
For 3 reasons really, 1) if anyone can pull off a project on this scale it's an authoritarian government on a push to diversify into tourism
2) unlike London Resort this project has specific rides named and shown in concept art. By that I mean the rides aren't just generic rollercoaster swirls as seen on the LR concept art, but are of recognisable models and rides.
3) this is the sister Park to Six Flags Dubai and Six Flags China, both of those parks while essentially now dead in their original guise are still moving ahead in one fashion or another, Dubai's rides are going to existing parks and China's Park is still going ahead under Sunacs brand. But my point is they were both projects that got to the point where rides were delivered and construction underway. Unlike say the LR again.
None of these are slam dunk proof anything will happen and I still think its 50/50 but I reckon its got way more of a chance than LR.
All fair points, but they are not without their counterpoints either:
For point 1), this can be right even while the project is stranding. Look to Ankapark/Wonderland Eurasia, for instance. It was built, apparently in a scheme to embezzle federal subsidies, yet it never operated as planned and the whole thing quickly folded. Authoritarian governments tend not to have the best procedures for quality control when money for big projects is handed out, and sometimes that's deliberate. Put another way, the Qiddiya developer probably wouldn't have got the green light to develop Qiddiya without strong ties to the government, question remains whether the development is meant as a way to actually develop the area or just channel funds to the developer.
There are plenty of reasons to question the viability of building the world's largest amusement park in the middle of a scorching desert in a country that barely gets any tourism outside of pilgrimage (to sites several hundred kilometers away), yet the funding is generous anyway. That doesn't sound like reasonable development to me, but it reeks of embezzlement, and in those cases the completion of the project is secondary to the main objective: siphoning as much investor money as possible, then hightail it.
For 2), the level of detail in dead-end skyscraper proposals in the UAE and Saudi Arabia in the past have jaded me a little. The old Six Flags Dubailand proposal also had quite recognisable coasters in it, and the proposal was detailed enough to include designs of individual sculptures in the park, yet it still fell flat. Making plans and drawings is practically free. Attaching some names to it is still cheap. Construction is the expensive part, and the one that's generally skipped in projects like this.
And as for 3), well, I think the existence of rides for the Six Flags parks despite the existence of parks to install them in, could itself be a warning sign. It shows that these projects have had a tendency to proceed well into the deliveries phase even while lacking crucial funding for the overall project. Six Flags Dubai did not have the means to complete the park, and while some work was done on site it was a far cry from anything operational, yet the coasters were still delivered. It's really strange that such a fundamentally flawed/underfunded project still got to the phase of ordering coasters from manufacturers.
Again one can draw parallels to the stalled skyscraper projects I follow with some interest. In Dubai alone, there are about a half-dozen sites where towers taller than 300 meters got well into the construction phase before money ran out. For whatever reason, construction was initiated even though the funding was nowhere enough to complete it. The only explanation I can think of is that the act of construction itself was used to build trust with investors. "Look, of course you will be getting your money back. There are workers on site working on the tower right now!". And then it gets to the seventh floor and the contractor stops working because of several missed payments, and the developer has suddenly moved to Aruba and is not available for comment anymore.
Or in other words: the contracts with coaster manufacturers could be allowed to proceed solely as a means to convince investors that work is underway, because manufacturing a coaster is relatively cheap and a very visible way to indicate progress, even though it has little importance to the overall progress of the project. It's easy for an investor to think "well, if they have the coasters underway, surely it means the park is doing well!" and then it turns out the coaster manufacturing is the only part that's adhering to schedule.
So yeah, overall I'm not convinced. That being said, I think the London Resort is even worse off. Then again, that might be because most of the tactics described above are illegal in the UK. LR might just have fewer tools at their disposal to build a convincing smokescreen.