It won't happen
Because government IT tends to be linked to legislation and government likes to fiddle with legislation. It can be bad enough for new systems like ID, but if your system has to correctly account for 40+ of legislation, then it can take over a year just to get all of the paperwork together.
And this is assuming that the legislation isn't contradictory (which it often is).
Then, once you have all of the paperwork together, someone needs to translate it from doublethink into something understandable so that it can be turned into software.
Then once it's turned into software you need to test it to make sure it is correctly accounting for the legislation. And then you can re-work it all to cover whatever the government enacted while all that was going on. And test it again.
Then it *might* be ready to go live, but then the civil-servants in charge of the project will say they don't have the authority and you have to wait for the minister to be available to sign it all off.
I'm amazed that some of the big stuff ever sees the light of day, TBH.
One year contracts would end up costing more money because most projects don't fit in a one year timescale, so you'd be re-negotiating all of the time and lawyers aren't free.
If you want your scapegoat, then just appoint one for each project, they don't even have to do anything, that'll be cheaper.
The way to reduce the costs would be for the government to correctly define what they want *first* and *then* to agree to not change any legislation while the system is in development, rather than do what they do at the moment, which is to just insert a clause in the contract telling the supplier they have to comply.