No, I'm afraid I don't know of a govt. sector company converting to open source. Although the place to poke into might be MITRE, since they have a very interesting dynamic as a place that supports government contracts, does research and works for the public good. If anyone has gotten into this sphere, I think it would be MITRE.
Things I'd think about:
- ownership of existing code is defined by your contracts. It depends on how you've set up your contracts in the past in terms of what rights you have to release your code as open source. Do not go past GO, go directly to lawyers.
security - there's two philosophies:
The more eyes the better - in a true open source project, you wouldn't be the only contributors. Theoretically, the number of good guys who want to contribute to using the product successfully will outwiegh the bad guys who want to exploit flaws. If the competence and abundance of good guys trumps bad guys, then you have a good formula for maintiaining a secure software baseline. This general philosophy is argued by a lot of the big names in the security business.
Protect secrecy at all costs - a basic assumption that you have enough in house experts that have been vetted by your organization that your closed organization will trump the hackers in brilliance and dilligence. This hasn't worked so well for Microsoft, but it's the policy by which a number of government agencies operate. I do know of situations where open source cannot be used because it's now public and the theory is that something which is known well to the hacker will be easier to hack than something that the hacker has never seen, because the development was done in a closed circuit where nothing leaked.
I am not going to make a judgement call on that one. In fact, I think the metrics are un-learnable, because I believe that ultimate examples of the second path are secret enough that stastics regarding the number of times that these secret systems have been hacked will never be made available to the masses. So how can you compare open source vs. secret development? The best you can do is compare open source to private sector development.
Lastly - the business -
Probably most important is - is this right for you? If you have been building products and growing them across multiple customers, then your move to open source will in some ways be a move from product development to solution develpment and consulting. You'll want to consider both technical issues - like how do you manage your code base if outside parties are contributing things you don't necessarily want in your baseline? And you'll have to change some of your business model, since you will need to explain to your customers how you are of value, even when you code is on the web for free.
I think these things are doable - but I think that's the biggest thing to consider - you want to still have a job when you are done, and you'll have to get your whole business line involved in creating the solution.