I'm not sure I agree with Lars' assessment. Largish piece of work yes... but 12 months.... crikey.... You could develop a whole new ACS in that time ;)..
As Dave suggested a more plug-in style architecture would allow progressive development, rather than a potential big-bang development.
As for a development based on the previous one... Noooo..... there are just some pieces of software out there that should just die... horribly... and stay dead ;)
