I'm mindful. The bus on Eglinton won't be disappearing either with the Crosstown even despite the much closer stop spacing.None of the options would replace the Don Mills local bus. To be competitive with the Yonge line, the DRL will most likely have 2km stop spacing north of Eglinton, like the Yonge line. At 2km spacing, you need an overlay bus service, because you're way beyond the ~400m suggested upper limit for local service stop spacing. Note that there's all-day bus service to duplicate the Yonge line north of Davisville, and there's even bus service duplicating the Sheppard line whose stop spacing is closer to 1km.
But it is the difference between running a frequent local bus service on Don Mills versus one that comes every 15 or 30 minutes.
The proposed alignment would intercept east-west bus riders from the Yonge subway and ferry them to locations downtown, but it won't do much for the people who's origin or destination is along Don Mills itself. Which is actually quite a lot of people (38,000 use the Don Mills bus daily at present, and 34 buses are operating the route in the morning rush hour) and destinations/employment.