The news item only mentions that the new book will be published in the Autumn.
However, what is not yet clear is acually when it's going to replace the existing one to form the core of the Life in UK Test.
Personally, I suspect there will be some transitional period of notice, just like the introduction of the B1 level English Language test for the ILR.
Currently the Life in UK test has no expiry, so I guess it's reasonable to suggest that if you've already achieved a pass certificate no-one should have to retake it just because it has changed.
That's only my personal opinion.
When the Life in UK Test has previously been changed/updated candidates were actually allowed to choose which edition they wanted to be tested on.
In my mind that would represents a possible alternative for any transitional period for those without an existing pass certificate.
In principle, I would consider it extremely harsh to expect people who are planning to take the test in readiness for their ILR application anytime soon to buy a complete new book and to study and pass a complete new test in such a short time frame and under the pressures of possible visa expiry.