And it was doing this by diverting riders from the Bloor-Danforth line to the Eglinton line. Which then dumps them on the Yonge line between Eglinton and Bloor. This doesn't really help much, just moves people around. The money putting Eglinton underground from Don Mills to Kennedy would be better spent extending the BD line to Scarborough Centre - then there wouldn't be the passenger demand to force Eglinton underground.
Either way, in order to eliminate an inconvenience for pretty much all of Scarborough, more money is going to need to be spent somewhere. The question then becomes where? From what I can tell, there seems to be 5 options on the table:
1) Keep Eglinton East at-grade, and run it independently from the Scarborough LRT.
2) Elevate Eglinton East, and interline it with the Scarborough LRT, creating a single thru-line.
3) Tunnel Eglinton East, and interline it with the Scarborough LRT, creating a single thru-line.
4) Extend the Bloor-Danforth Subway to STC, and leave Eglinton East at-grade.
5) Extend the Bloor-Danforth Subway to Sheppard & McCowan, and leave Eglinton East at-grade.
Personally, I favour Options 2 or 5. Option 1 doesn't really work from a network perspective. Option 3 is an unnecessary tunnelling expense when less expensive options are available that will achieve the same result (grade separation). Option 4 is good, but extending the subway that extra stop really simplifies a lot of network connectivity issues, particularly with whatever is placed along Sheppard East.