Personal opinion but eliminating credit for time as a temporary residents and intent to remain in Canada may be more likely. 4 out of 6 years may also return. The current system allows people to leave right after 3 years which is not a huge benefit to Canada and creates significant liabilities. We’ll all need to wait and see.
Leaving aside the posts here that hew more to the "I wish it were so"* rather than likely, I think the main points are:
-changes that can be made quickly with less complicated legislative steps are more likely to happen;
-tightening regulations / rules by eliminating some bits that are relatively minor (in the grand scheme of things) are also more likely - and also more likely to be positively seen by the public at large.
I'd rank your list as amongst the more likely options available. With my slight comments:
-I think priorities will be elsewhere for a bit. Maybe not for long, though. Anythign 'border' 'security' and the like will be higher up.
-announcing some 'tightening' about physical presence after applying would be easier/quite effective without the (quite complex) legal issues about how to show 'intent to remain.' Allocating low priority / extra checks for all files where the applicant doesn't remain in Canada - basically just slow walking all such apps - would be a nasty but effective bureaucratic move. (It would be potentially open to a lot of mandamus requests, but just call them all 'complex' and wave hands at security issues; oddly possibly
less vulnerable to being overturned. Given the backlog in refugee files etc they can change processing priorities and slow walk some things)
-remove the time as a TR - wouldn't cause such a hue and cry as moving it to four years, but would be fairly simple legislatively and fairly popular. (They could also just change the ratio, or limit it in some other ways, like minimum three years as a TR and must be for work)
-4 out of 6 years - my only reservation here is I think it would be fairly unpopular, or at least less popular than other measures, and kind of 'not done' to just nakedly reinstate what was done before. But on the other hand, fairly straightforward.
*Nothign wrong with "I wish it were so" type posts, just I thought the interesting part of the original question was how likely in the nearer term.