Actually, I was talking to Michael about this, and it seems that it could be done rather easily (compared with other things

). From what I understand, when using the three types of track (rails, e-mails and monorail), the following is true:
E-Rails are a seperate type of rail, that just happens to look similar to normal rails, and allows trains from normal rails to run on them (which holds true under the rail, mono, maglev system, apart from the train sharing), and thus act like the monorail for construction purposes.
That said, they also have their own graphics, as we all know that they are not an upgrade from normal rails.
So, it stands to logic that the depots will work in the same way: There is a seperate depot for the rails, the e-rails and the monorail, the only thing being that the rails depot and the e-rails depot share the same graphics.
Therefore, it should be possible to change the graphics of the e-rails depot into something more modern, perhaps something that looks like a diesel maintenence shed. Whilst it would not be possible to make it bigger in size, it would look a bit better from a aesthetic point of view.