.....But in the AF447 disaster the ELT might have allowed the aircraft to be found sooner, ....
Sadly, because AF447 sank and salt water virtually prevents any RF transmission (other than VLF or ELF as used to communicate with submarines), it would not have helped.
I think the FDRs have a sonar type transducer 'pinging' away to allow location underwater but I don't thing the standard ELT does?