I'm not certain if this piece if news has been mentioned here but Berita Harian, a Malay language daily in Malaysia is reporting that flight MH370 did indeed turn back from the SCS. The RMAF chief Rodzali Daud is quoted as saying that the last time the flight was detected by military radar, was at 2.40 am and somewhere around Pulau Perak (Perak Island) north of the straits of Malacca. It was flying at 1,000 metres lower than its 10,000 metres altitude when it turned back. Apparently the Singapore ATC also detected the plane.
The source:
Berita Harian | Operasi SAR ke Selat Melaka
I don't know how credible the news is but MalaysiaKini is also reporting it.