It has already started, meetings to agree local plans for submission are being cancelled up and down the country, even to agree reg19 draft plans, the incentive of a 4yHLS not being enough, many authorities want to be seen as abandoning large housing sites and Green Belt releases before the May elections, as Hertsmere and Ashfield have done, as the 4 year rules only applies to out of plan sites, not to the 15 year requirement for sound plans, hence it is a silly incentive that incentivizes nothing except planning application refusals.
A proper incentive would be to only apply the new standard method only if and when a local plan is adopted, to carry on with plan making, and where necessary review plans once they are adopted. Less housing but at the very least at least it wouldn’t further incentivise the ongoing collapse of plan making.