Part of the reason why we aren't getting "proactive" overpasses/interchanges is that there is no money. Look at Stonebridge - the hwy 11 interchange is
finally being built, because the developer has accrued enough development fees from property sales. Meanwhile the cost of construction has risen as well, so the city has to kick in more of their portion. I'm not impressed with this arrangement, either.
There is little money up front to drop in $30 mil interchanges where they will eventually be needed - that money is going now to things that needed interchanges years ago. Once Brighton etc. is online, it'll be a net benefit to the city - after the costs of city servicing and local roads are paid off, which takes a long, long time in low-density greenfield suburbs. Then there might be some extra $ for infrastructure upgrades (which will probably go to neighbourhoods who have been waiting for upgrades longer) or if the city can manage to convince the province to kick in highway funds.
If you look at it from some angles the development pattern represents a ponzi scheme - new neighbourhoods are built to generate money to fund growth to build new neighbourhoods. Meanwhile established older areas decay even while they are a net benefit for the city since their up front costs are paid off ages ago. I may be a bit bitter on this
I agree, it's not a great way to build a city, and a conversation is needed on stable, forward-thinking funding. It probably involves raising taxes and curbing greenfield development below the current level of 85% of new builds, which is why we're not having it.