I don't really mess much with computer programming. I know a number of people have managed to write programs for controlling the ACIII remotely using the unit's webserver capability. It might be a bit unintuitive when compared to what the Elos might offer. Still, I've seen some rather cool programs. One guy wrote a program that takes the hourly forecast from Fiji and uses it to control the temp, lighting, and pumps in his tank. Browse the Neptune forum and you can find similar examples.
As far as expandability to new technology, the aquatronica and profilux units do have a few cool peripherals that make them stand out, such as their peristaltic pumps and 10V DC control. The profilux has a cool modular design that's pretty appealing, but it costs so much expanding it that I question the worth. I have a feeling Neptune will come out with similar peripherals in the future. The aqua-surf is one such example. If you like to fiddle with things and have a decent electronics/programming background, then you shouldn't have much trouble doing all kinds of things with the ACIII or ACIII Pro.