I'd actually bet that if they did make a Trident 2 that only worked with apex3 or apex2 with an expensive add on module, they would make MORE money because people would grumble a whole lot and then upgrade.
I'll assume Neptune has a good idea of what things they are working on and what is coming in the next 24-36 months for them. They obviously have the headroom with the current hardware to match anything coming.
AFAIK Neptune has never said, "we're close to running out of memory and/or processing power."
So it's very likely the A4 would be the new hardware and internals. That's likely 3-5 years off. Most in this thread won't even be in the hobby when that happens