if both trains are back to back what u saying will be correct. For example: Blue mountain and Cheran can equally split the stops as they are almost back to back. Yercaud present for intermediate beyond ED. Here the caterance and timing difference is too much. so kind of early arrival and late arrival so it will be very tough to reduce the stoppages. What u said can be applied with TBM NCJ SF and Ananthu reducing halts in NCJ-MDU section and sharing loads equally once it becomes daily. Even though MAS ALLP present for ernakulam I dont think load split will work for 12695/6 & 12623/4 as their caterance is totally difference. On the case of TBM KCVL regularised to daily (alternatively TBM SCT can be made daily and extended to KCVL) and MS kollam mail extended to KCVL what u said can be done between VPT and KCVL....
more... as pothigai there till SCT taking load for chennai. Kerala is highly urbanised than TN and fall in single line compared to branching in TN. so without having proper MEMU i dont think reducing stoppages will be possible.