IIRC, in RMTransit's video on Frankfurt, he explicitly mentions that its Stadtbahn* was a direct inspiration for Calgary (and Edmonton). One example from the city's N-S axis:
- Dornbusch - Sandelmuhle, after the N-S line exits its underground tunnel in the city's core; the trains run in the centre of the city's main N-S street (Eschersheimer Landstrasse), thus comparable to Eglinton and Finch. ~3.5km, 9 minutes, 6 stops ~= 22km/h. This is with generous stop spacing, so if you were to remove some stops then I would imagine this would approach 30, so it shows there is a pathway to get near these numbers without grade-separation or tunneling. Given how Frankfurt is more compact, there isn't any pressure at all to sacrifice accessibility for speed. I never had any complaints getting from Hauptwache to Kalbach in ~20 minutes which was near the "border" of the city.
This section was supposed to be originally tunneled, like the southern portions of the line, but wasn't because the city didn't have the money to do so. There is no push by anyone to tunnel this section because there is not really any realizable ROI (beyond saving the deaths of 1-2 people/yr who will come into contact with the train. The main consequence of not tunneling this section is that it really divides the neighbourhoods it crosses in two. The last time I was on Finch near Milvan Rumbie, there were 2 people that jaywalked across the road. While less likely given the lower frequencies, I fear that eventually there will be a crosser who gets hit by a train that will rollback whatever progress is made on speed.)
- Sandelmuhle - Gonzenheim (Bad Homburg); no longer on the centre of the street (mainly on the sides as the train exits the "city" and moves through the greenbelt towards the surrounding towns), ~8km, 12 minutes, 6 stops ~= 40km/h
Frankfurt also has a situation comparable to Eglinton - which is the ~2.7km U5 expansion into the new(er) district that is the Europaviertel (planning to provide ~30K jobs + ~4K housing units), which is just west of the Hbf. The investors wanted an underground line throughout the district, and used the Eschersheimer example above of dividing a neighbourhood in half as their case for why, but the federal and state gov'ts viewed this as too expensive and refused to fund the project. The result was a half-and-half compromise. Issues e.g. tunnel boring, bomb fragments, have resulted in the start date projected to be in 2029, versus the originally intended date of 2022. That might actually make Eglinton look good in comparison!
I would imagine there are lots of lessons from (East) Berlin that are applicable on how best to deal with our reality (but I don't know too much here). Since the DDR essentially had to do Transit City en masse to enable the development of housing given their financial situation (also in other cities e.g. Halle-Neustadt). What seems to be the trend is average speeds of ~17-20km/h with stop spacing generally of ~600-700m. Again, with these numbers, you can argue that there is a plausible pathway to near 30 with larger stop spacing. Albeit I believe planners view the impact of a LRT stop as being a 500m radius, so too far spacing might dilute the development / land value benefits it would give.
Stadtbahns are also comparable history-wise, given the German cities that pursued this wanted U-Bahns but couldn't afford them. So the Stadtbahn was the middle ground that could potentially be converted down the line, but they've largely all given up on this dream. So while I agree that a conversion would be great to serve the future needs of the Golden Mile, history would tell us that all you need are one or two large recessions for that idea to probably evaporate from the mainstream for a half-century (assuming government fiscal accountability returns to fashion).
I believe you can argue that Seville and Malaga's systems are also new faster "light rail" of the 21st century. These are comparable to Eglinton Crosstown, since while primarily/all underground, they use low-floor tram vehicles. I really liked Tampere's LRT system but it seemed to be more comparable to Waterloo rather than being subway speed.
*The distinction between an U-Bahn and a tram in Frankfurt appears to be high-floor vs low-floor vehicles rather than their level of grade separation. There is a brief part of U5 where its tracks share traffic with cars.