Don Mills isn't suited for a LRT. There is hardly any opportunities for development along the entire corridor. It's all built up and isn't commercial oriented. A Relief subway is more suitable.While that is great and all, the problem with that TC mindset for corridors like Eglinton and Don Mills is that ridership is already far too high to not invest in faster rapid transit. For Finch West, Jane, and the Waterfront it's a different story, where revitalization is absolutely necessary. Hamilton and KW as a whole also fit into this category of needing to revitalize key transit corridors without needing the huge speed boosts provided by subways or High Floor Light Rail.
To clarify, Light rail on these specific corridors should still be fast (even though the RoW arguably cheaped out on iON, it's still at least 30% faster and 200% more reliable than the 200, and those numbers could grow in the near future as the teething problems are resolved), but it doesn't require suburban subway speeds.
Eglinton is debatable. Do we really need another subway across the city that would take well over an hour to make any trips from Etobicoke to Scarborough? Yes ridership is high but is there really a reason to confine them to Eglinton? There's no real destination along the route that requires people to stick on Eglinton. The Yonge Line is crowded only because it is the main way out of the city. If we build the Relief Line to Steeles/York Region, the Yonge Line will see a huge drop in ridership.
Personally, I rather see an integrated RER system for travelling between the two ends of the city. Subways are way too slow to get from Kipling to Kennedy. There is also a lot of development opportunities along Eglinton that would help the LRT case