Yes Stealth they've discussed (re-)adding an SRQ before, but the current batching system works well for the efficiency of the ride and doesn't lend itself to SRQ.
And this is the thing. SRQs serve two purposes:
1. Improve utilisation scores (the percentage of seats filled)
2. Give a mild improvement to guest satisfaction scores
The first point is the bigger one. SRQs simply do not improve throughputs meaningfully. Let's say Hyperia sends 40 trains an hour, and 1 person from the SRQ goes on each train. That's an increase of 40 people. And without an SRQ, a good batcher could probably fill some of those seats anyway. So it's not really significantly meaningful.
Improving utilisation does ultimately look good, and will increase the total ridership, and so ever so slightly improve the "rides per head" score - the average number of rides ridden per guest. But it will be marginal.
As for improving guest satisfaction/experience. The number of people using or benefitting from SRQs is generally a tiny proportion of the number of guests. That's not to say parks should ignore them, but it should be remembered that it's again minimal gains.
SRQs need to properly and sensibly integrated. That's why Hyperia works. How does one, for example, introduce an SRQ on Nemesis Inferno? There's no clear pathway to the station for it. Any potential batching point is too far away. Similar stories for Swarm and Colossus.
As mentioned, Stealth has that natural point, but the current operation of the ride doesn't lend itself to having an SRQ. You could put it into some flat rides, and share the space with Fastrack, but that requires good batching. And bluntly put, Thorpe don't have enough staff who care to be good enough batchers (a trend common at many parks, for the record).
So yeah, I don't see any rides having SRQs retrospectively (re-)added any time soon.