The ARINC 653 scheduler was funded by DARPA, a project aimed at satellites. Now that it's there out in the "open", certifiable, yes, some people who might not otherwise get an opportunity to "play" with aviation technology have a chance to get hands-on experience and possibly contribute something. Not totally "free", some premium tools for a development environment are sold at a price, but accessible. I stumbled across it when I was looking for a virtual lab, a network simulation to better understand AFDX (which I didn't find).
From the specs I see it's impossible to play any classic ethernet tricks like manipulating ARP tables, switches have a fixed table of MAC addresses, this is not a security feature, but to lower latency, in a network where all components are known. Switches also do some kind of traffic policing as I understand, again not for "anti-hacker security", but to ensure bandwidth is available I assume. Anyway, it was interesting to learn more, I had a rudimentary understanding of engines, hydraulics and electrical systems etc, but not the new AFDX parts of aircraft
Frankly I don't see how anything could be "hacked" without physical access, without connecting hardware in, say, the avionics bay. And that is not the "hacking" the GAO or newspapers had in mind.
The wildest scenario I could imagine for "wifi hacking" (without physical, hands-on access to critical components) is, that there could be undocumented backdoors or protocols in the satcom equipment (to which pax terminals already have 2 way communication) left behind by careless manufacturers, for their convenience (happens more often than it should). Which again is not critical for flight. And even the worst kind of "hacking" scenarios I could imagine as feasible, signal spoofing, are essentially all about altering information as it is presented to pilots, and pilots routinely deal with unreliable information. The latter is probably the biggest advantage they have over automation, and the reason why they are there.
I have no problems understanding the benefits of integrated modular avionics, although I can understand that at first sight people can be dumbfounded why pax entertainment services need to be physically connected to "avionics" (it's labelled IMA, not integrated modular everything). An "air gap" is a good practice for security, yet I think what some people, including me, can misunderstand, is that they interpret the concept of an "air gap" too literally, and get confused by repeated somewhat misleading news reports.