Nah, the land behind Swarm is fine and ready for a coaster, unless there's something seriously wrong with it.
You don't need that long for the land to before you can build on.
If we take a look back in 2005, none of the infilled land was present. That includes Saw, Saw Alive path, Swarm, island behind Swarm and the road linking up the old Treasure Island to the Engineering area, plus Hyperia's infilling.
2005:
Google Earth allows you to look at 3D models of current buildings too. It's not accurate, but gives a rough look:
Fastforward to 2008. The land for Saw was infilled and settled (completed by 2007). The park are starting on Saw Alive pathway, and the two islands.
What's noteworthy is that Saw's had been completed and constructed on between 2005-2008, and neither Swarm nor the other island are complete yet.
2008:
Go again to 2010 (annoying Google Earth doesn't have yearly looks). Saw open, Saw Alive pathway being used. Swarm island complete. Adjacent island almost complete.
2010:
2012. Swarm opens and Thorpe flops, apparently. Tidied up of Swarm island land. The adjacent island is now completely infilled, even featuring some of Swarm's layout. All is golden.
2012:
I also haven't mentioned the building of the hotel. We see nothing in 2008, the land almost complete in 2010, and by 2013, the hotel exists.
We can also see with Hyperia, some supports were built on reclaimed. Compare 2024 vs 2022.
2024:
2022:
The island behind Swarm has been complete since 2012. Whilst no doubt there is a level of needing the ground to settle, it will be settled by now. If not, there's major integrity issues and the park would either be actively doing work to resolve that, or not be considering the area for rides at all.
However, before Swarm's failure, a coaster was planned there for 2015. A coaster was considered there for 2020. The project that ultimately ended up with us getting Hyperia was considered for there. The park have actively considered rides there, and as I understand, it's the front runner location for the next major investment.