I understand ... although having jumped from AD&D 1st edition to 3rd, I can say that the 3rd edition rules are much more coherent, and thus more easily programmable. Fewer exceptions, more natural progressions, less arbitrariness. All that and lots more flexibility, too.

No one says you need to support everything - I would just encourage you to use OGC as your basis - which will allow you to continue advancing your support for OGC and allow some really modern games, too. What I mean is that you can support a subset of OGC to start with, and add support for more stuff as time goes on.