Upcoming Proposed Benefit Changes

many claimants are aware of a select committee meeting on Monday 7th upcoming, which might give indication as to whether Labour will adopt the changes proposed by last government on PIP and on WCA. I know it's in the realm of speculation but let's say the changes are adopted to some degree or other. If the plans to make the WCA harder to pass are adopted would it be likely, or even legal that the DWP just notify current claimants of ESA, say on the benefit for mental health or muscular skeletal conditions as many are, that they no longer qualify and tell them they must claim UC? Or would it likely be done by only adopting the new changes for new claimants initially, and for current claimants to be reviewed under the new rules when their review date comes round? Or could they nobble the managed migration to UC by making existing claimants apply for UC but when the DWP check their claim apply the new rules at the start of the claim and for example tell claimants the health conditions they have stated on the claim form suggest the cannot claim the sickness/health elements of UC as the rules have changed and they are effectively going onto the UC equivalent of JSA?
Similarly, with PIP are any new changes to criteria etc likely to be applied clerically for existing claimants across the board? Or again is it likely government procedure would dictate they apply changes to new claimants and again to existing PIP claimants as and when their review date comes up. I'd appreciate any info on what would and would not be legal or the norm in this situation.