In the case of HWY 10, I don't think that stopping at a RIRO is good enough - it easily has the traffic to justify a full new freeway. Using the
MTO iCorridor Tool, you can see that the 2019 AADT across the corridor between Brampton and Orangeville ranges from 23,000 to 40,700, which is comparable to the QEW between Niagara Falls and Fort Erie. For perspective, MTO starts to consider the construction of a freeway once AADT passes 10,000. The numbers are likely significantly higher than this now.
I think the province is ultimately going to end up extending HWY 410 on a new alignment instead of converting HWY 10, given that the province is going through all the effort to build a new alignment to meet HWY 413. You wouldn't have to deal with the issue of having to bypass Caledon Village and create access/service roads for all of those properties that front HWY 10, but it would be a new build highway and subsequently very expensive. I do agree that MTO should be looking at more compact designs similar to the Morriston Bypass to save cost. Large grassy medians are nice for future-proofing, but sometimes it makes more sense to keep it compact when property values are so high.