I've created a place holder spec. here: http://www.xtuple.org/node/2918
I agree with the notion of using operations to handle processes in principle. Keep in mind, however, that only the Manufacturing Edition supports operations. We wouldn't want to do anything that takes existing functionality away from PostBooks users, so the use of operations to handle outside processes would have to be optional somehow.
In general my strong preference would be to implement a solution as an Extension package first, then port it to the core once it has been vetted out and proven. Also if it turns out there are any manufacturing edition dependent elements, like bill of operation support, it would have to be scripted anyway. Finally, there are long term plans to port Standard Edition and perhaps even significant sections of PostBooks to Extension packages as well.
J2m, do you want to take the lead on this since you're one party who is actually prepared to commit resources to do the development? You already have access to edit the specification. There's a lot of great ideas here but as is always the case in the world of open source, the people who ultimately either pay for or do the coding are the ones who ultimately make the decisions concerning scope. We more or less play the role of referee.