Eglinton is going to be running different LRVs though. Eglinton will have Bombardier Flexity Freedoms and Finch is going to be using Alstom Citidalis Sprints (same as Ottawa's Confederation Line and the Hurontario LRT). They were supposed to be the same, but after the streetcar mess, Metrolinx changed plans and moved to Alstom trains for Finch. Hypothetically you could use them on the same line, as they have the same track gauge, but the maintenance yard at Finch isn't going to be built to support both kinds.
It is weird they keep showing Flexities in the renderings though, given Metrolinx has been clearly using a Citidalis in all their press materials.