Mumbai-Chennai Arm Shall be definitely touching Pune. Pune could have been covered with Ahmedbad-Mumbai project,was but left out to contain costs. Nothing had been heard so far about the exact route towards Chennai, which is expected to be more or less parallel to the existing line to avoid land acquisition to the extent possible, thanks to extreme difficulties if land acquisition. Actual route depend a lot on what the survey report and market study says.
My wish is to go elevated over the Mumbai--(980) Bangalore--(+350=1330) Chennai Expressway/ Highway. This route may be 1330 km long about 50 km longer for Chennai (1280 km) and about 230 km shorter for Banglore (1210km) than the existing rail route may be a better option...
more... from point of view of better area-coverage, revenue & patronage also. Bangaluru probably have more air traffic than Chennai and higher number of passengers are expected from Bengaluru.
Historically there were 4 Major cities- Kolkata-Mumbai-Chennai-Delhi. At the time of independence probably Madras was more populous than Delhi. (1971 figures as far as I remember are 72-59-25-36 lacs respectively.). From national integration point of view, these 4 cities suited well as 4 Metros of India.
But today the above Metro Club is irrelevant. Today there are 3 metros around and above 1.5 crore i.e. Mumbai, Delhi, Kolkata. Next is cluster of 4 in 75lacs-1 crore band i.e. Chennai, Bangaluru, Hyderabad, Ahmedabad. Then Pune, Surat are 50lacs+ and so on. When our leaders speak of metro cities of nation, they say Chennai to represent south. But today Bangalore and Hyderabad had grown up and are catching up very fast and cannot be neglected in matter of representing south India.