Would be more efficient to run all services to Queens Quay (rather than Union), and increase 509 services a bit instead.
I've always wanted them to go with that. I think once the southern part of the tracks on Spadina reopened, but QQ was still getting finished up, they ran it like that for a month or so and it seemed to work great. I think they also did that for the duration of the Pan-Am Games, and once again, I thought it was excellent. It seems like the most logical option--service to CityPlace gets a massive and much-needed boost, then there's a very easy transfer to connect to/from Union via 509. In fact, I usually do that myself--it's usually a fair bit faster to board a 509 if it shows up first at Union, hop off at Spadina, and walk over to the loop; or conversely I take a southbound 510 to Queen's Quay, then either a 509 will show up first or I'll end up getting on a 510 Union anyways. I've found it shaves quite a bit off my travel time. Hell, I see a lot of CityPlace dwellers just get on the 509 instead of the 510 at Union and walk the few minutes up to Bremner, as I often do when going to that Sobeys instead of waiting an extra 10-15 minutes.
It's a shame that we place such a negative value on having to transfer, and try to shoehorn as many possible trip patterns as possible into one route where it doesn't make sense, all for the sake of keeping people on one vehicle. I agree that having to make transfers is definitely annoying, but the benefits here certainly seem to outweigh the risks...cityplace riders benefit, western 509 riders (Bathurst/YTZ, Fort York, Exhibition/Liberty) benefit, and tourists boarding at Union during the summer will be less confused (the number of times I've seen a huge line, barely anyone gets on the 510, the next 509 overflows and half get off at Queen's Quay...).
And it's largely run that way already, anyways--I can't count the number of times I've seen vehicles distributed like that nextbus screenshot, with the QQ/Spadina to Union stretch utterly barren of 510s for as long as half an hour for no discernible reason. Certainly not constant, but a very frequent occurrence, even during peak. Even the King-QQ leg is bad at times--I've waited 20 minutes at Queen's Quay and Spadina during midday waiting to go North a number of times, called an Uber, and had it arrive still with no sign of a car...at least doing this would fix the King-QQ leg. And of course, contacting the TTC with a service quality complaint of 25 minutes vs a few-minute headway yields the standard echo of "We're sorry for the wait; service planners and route supervisors monitor routes and schedule service appropriately"...what a joke.
One benefit of the current mess of service on the southern 510 is that I've made good friends with the staff at the relatively-new Queen's Quay and Spadina Starbucks, having cumulatively spent many hours there waiting for the 510...I'd miss that!
