Back onto the TRR speculation - in particular this 'sensor' thing.
(cue a Roachie groan) - Wonderland's Snowy River had an "invisible beam" infra-red sensor, like we see on many water rides, mounted at the top of the conveyor. There were more IR sensors placed throughout the loading zones. The PLC wouldn't allow the conveyor to lower the next raft if the zone immediately after it was occupied, like any block system (Although Wonderland's conveyor reached it's peak and then lowered back down into the water on a slope, rather than allowing the raft to tip off it).
I'd always been of the opinion that there was a sensor at the top of the TRR conveyor that wasn't functioning properly - however it is possible to alter the PLC (or fool the sensor) if it is malfunctioning. Judging by some of the things said above, it seems like this may not have been the case - that there wasn't a sensor there at all.
For my own uneducated opinion, the slats certainly contributed, but the slats don't cause this issue on their own without several other factors.
The 'inexperienced' staff member cited by media immediately following the incident isn't portrayed clearly, and while i don't know all the facts, what i believe was that the cast member was not responsible for a panel - they were more of a loader\unloaded role - but that they had completed the required training for the task they were undertaking.
And for me, regardless of the placement of the e-stop for the cast member closest enough to witness this occurring, by the time you would notice the raft rising beyond normal, the time it would take you to hit the e-stop, it might as well have been located at tiger island. the raft would have tilted beyond recovery point before any stop could be engaged. This is why sensors and PLCs should have prevented the rafts from ever getting that close in the first place.
The rails underneath the water in the station are also, for my thoughts, contributing factors - they were trying to rectify a risk (boats tilting while guests step on and off) without thinking through the flow on consequences. In this circumstance the raft in front was immovable, which in my view is what forced the raft to flip.
The pumps themselves are pretty powerful beasts. I've seen these things suck up some very large objects and spit them out the other side. If the rafts were capable of floating out of the station under load (which it would need to, for them to have operated it all day) there was sufficient water pumping through the attraction and the offline pump probably wouldn't have made any difference.
Wonderland also stopped the rotation of the stationhouse. On many rapids rides i've been on overseas, i haven't yet come across another park that has done this. The turntables clearly prevent other issues, but they of course contribute to slip and fall accidents on behalf of a guest and in today's litigious society, if you could come up with a way to load the ride without the turntable it would probably be something you'd do - but by stopping the boats in the station, you're causing other issues to pop up elsewhere, and unless you can think of, and address them all, staying with the manufacturer's (or best practice) design is probably the better way to go. (yes, i realise the irony of me saying this here) and it gives me pause to wonder whether Wonderland's version could possibly have seen similar risks as it wore on (another 14 years wear on the slats - could they have done similarly to Dreamworld?, might they have installed rails?)...
anyway - that's my 40 cents.