Yes, of course it is a struggle to get it into a part platform, and it is unlikely to be a "specific" proposal.... if it were to make it in.
If memory serves me well, the Tory's are weak in Toronto, stronger in rural Ontario. Liberals are stronger in Toronto, weaker in rural Ontario. Most likely the Liberals will be more likely to take Toronto for granted, while if the Tory's want to have a chance to form a majority government -- they have to make inroads into Toronto (and suburbs). I believe that this subway construction -- or -- go/subway integration where go is electrified and used as express in Toronto (as well as current usages) -- it has to be pitched as vote-getter in Toronto (and region).
If it did make it into the platform, it would likely have to be a catch phrase like (3 subway stations a year for 10 years, or GO/TTC integration (for suburbs and Toronto).
If by some miracle -- it could make it into the Tory's platform, then the Liberals would have to make a counter proposal -- or risk bleeding urban voter support.
ALL of this thread though is a BIG IF. Selling it at Miller's level is probably insufficient -- even if you were to convince him -- and I have my doubts there.