It will be a rather fine line when it comes to the earnings. The train capacity may decrease by moving to a Talgo rake. But at the same time there would be considerable savings in Energy and maintenance costs ( Talgo is projecting about 30%, but it will be less that that). With that included, the earnings may not take a big hit.
Talgo may not be a viable alternative at the outset for the Mumbai Raj, or the Bhopal Shatabdi due to the loss in capacity. But it will be a better alternative for many of the Shatabdi's running on non-high speed routes like MYS/SBC-MAS, Pune-SC etc.
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Actually a huge capital investment would be required for upgrading routes to run the Mumbai raj at 160kmph. For the HWH and Mumbai routes alone, IR has projected an estimate of 10,000 cr for upgrading the routes to be 160kmph fit as it would require actual relaying of tracks, changes in alignment in some places and many more large scale works to enable the long, heavy rakes to run at high speeds. It is not a short term project.
On the contrary, Talgo rakes will require a much smaller expenditure ( for initial rake purchase and setup of maintenance facilities) and can be used on any of the trunk routes and most of the important non-high speed routes with very minor modifications on these routes. They can run at higher speeds on existing routes and will reduce maintenance and energy costs considerably.
But Talgo is only a short term solution.More importantly, the LHB technology itself is now over 25 years old and stainless steel coaches worldwide have been replaced with more efficient, lighter aluminum and alloy coaches. By the turn of the decade, IR will have to move to these newer ones to reduce operational costs ( and the savings it would get are considerable). Trying out Talgo rakes would go a long way to help IR to transition in to the next generation.