I'm not sure how to read the regulation for aircraft older than July 2008 - it seems to say they must have an ELT but later aircraft have the option of a PLB. If they had put an "or" at the end of bullet 1 it would have been clear.
The AMCs and GM don't expand the options - just more practical detail on things like when to change batteries.
Either way they cost money whereas until now there has been an exemption for non-commercial.
NCO.IDE.A.170 Emergency locator transmitter (ELT)
(a) Aeroplanes shall be equipped with:
(1) an ELT of any type, when first issued with an individual CofA on or before 1 July 2008;
(2) an automatic ELT, when first issued with an individual CofA after 1 July 2008; or
(3) a survival ELT (ELT(S)) or a personal locator beacon (PLB), carried by a crew member or a passenger, when certified for a maximum passenger seating configuration of six or less.
(b) ELTs of any type and PLBs shall be capable of transmitting simultaneously on 121,5 MHz and 406 MHz.