It's been talked about before, but I've firmed up
what I really think the most appropriate course of action for Scarborough is. Essentially the Wye proposal, using high floor LRVs to reduce conversion costs but maintain commonality and allow less than total grade separation. IMO it would be entirely possible to market this thing as being the same technology as the Ontario Line at this stage (yeah, that's probably using trains not intended for street running, but intentions aside current High Floor LRVs and light metro units are basically identical in size, capacity and performance).
I'd drop the RER Lawrence station but re-locate Agincourt and add one at Finch and time construction so that the SRT shutdown is delayed until (short of the trains falling apart
) the Eglinton East extension opens first and bus priority (if not fully dedicated lanes) is available on Kennedy and Progress.