Because Erode-Karur-Dindigul was in Diesel from several years but after August 2018 or December 2018 trains will start running in ELoco and Salem-Karur-Namakkal is also being electrified.
Trichy-Thanjavur-Karaikal is also being electrified.
Tenders are out for Salem-Dharmapuri-Bangalore line and Thanjavur-Mayiladuthurai-Villupuram line. Hope they complete by 2020