I think the suggestion is that they play 105 overs per day - under lights if necessary so that's 420 overs minimum instead of 450 now. Obviously, the loss of a day due to weather will have a more dramatic effect.
The motive is to generate interest. Personally, I'm not sure 4 days instead of 5 is much of a change. What is needed is the regulation of pitches to ensure we don't get 600 plays 500, then 200-2 dec and a tame draw after the team batting 4th bats 70 overs for 160-3. In English conditions, most Test matches are decided in 4 days anyway - many in 3. In the subcontinent though, bowlers need a better chance on flat, slow pitches.