Many things you say are true, such as system design is more important than language choice when it comes to scalability. As long as you're I/O bound, your memory throughput and CPU utilization doesn't matter, for example.
I have two additional comments:
1) There exists a large, open source, game server engine that attempts massive scalability. This was Project Darkstar from Sun, since then moved off of Sun/Oracle into the RedDwarf Server project. By trying to be general, it unfortunately lost out on the scalability part.
2) Without a specific game with specific performance requirements and specific rule sets, I fear that your system will not actually solve anyone's particular problems.
Yes I noticed darkstar several years back. There were several other attempts also that I can't remember off the top of my head. And yes I think almost all of them tried to solve too many problems.
I'm actually talking to some local indie game companies in an effort to continue the development within the context of a real game, I think it's important to stay within something real. But I disagree that an engine has to be specific to just one game. There are problems common to all massive multiplayer games. If you can solve those with the right abstractions, then it's reusable across different games.