Technology is not a real problem here. The problem is the cost involved. With such projects, there is no scope of cost saving as every single aspect of the tunnel must be constructed very precisely. Even the tiniest mistake will risk hundreds of lives. The Swiss project in the post cost an estimated 66000 crore Rupees for the 57 km tunnel. Given the treacherous conditions in the western ghats, the cost will be even more. We simply don't have enough money to take up such projects. Also, with the kind of fare structure followed in India, it'll take several decades for the railways to recover this investment.
Another problem is the use of non A/C sleeper coaches....
more... Beyond a certain length and depth of the tunnel, it is not safe to use non A/C coaches as the air quality will degrade substantially. It'll be a huge economic burden on the railways and the people as they will not have any low cost travel means.