My preference would actually be to do both. Have a 'common' line up to just north of Eglinton, then have one branch veer east over the Don Valley using the CP ROW, then up Victoria Park to Sheppard. Turning west at Sheppard, it would connect to the existing Sheppard Subway at Don Mills.
The second branch would continue northward under Don Mills until just north of Lawrence, where it would emerge in the Richmond Hill ROW, and run parallel to it all the way to Richmond Hill Centre (dipping under the Doncaster Diamond).
Use the funding that would be allocated for the DRL North for the Victoria Park branch, and use the funding that would be allocated for the North Yonge extension for the Richmond Hill branch.
You wouldn't need super high frequencies on either of those branches (4 mins during peak and 5-6 mins outside of peak would do it), and with ATO the frequencies on the common section of the line could be managed pretty effectively.