Hopefully it is not self-serving to bump my own thread.

Although no longer working online, and they've removed the FAQ/ redemption table, there is still a concept of "Upgrading with Points" for domestic MAS operated flights.

Under that scheme, Y fares require 0 Enrich Points to upgrade to J.

The (predictable and reasonable) snag is that there needs to be I class available to book into and you have to pay the additional taxes.

Edit: The problem with this workflow is that when you upgrade and get issued an I class ticket you then lose your ability to change the date or even get access to the standby waitlist at the airport as it requires a system downgrade back to Y. The downgrade process confused everyone I talked to and I was shuttling between the ticket desk, standby desk and ticket office to do this yesterday. The taxes one pays for the upgrade (RM166 KCH>KL, RM71 KUL>MIR) are of course lost if you cancel your ticket or force a downgrade for waitlist purposes which is what I would have expected.