Update on this - they are no longer requiring a pre-registration on arrival for the e-gates
I went looking for the counter on Sunday afternoon on arrival to KLIA
A roving immigration officer explained that they had done away with this requirement - and asked if I had filled out the MDAC. I showed him, he said that's all that's needed - and walked me over to the e-gates - took my passport, scanned it - and I was through

So if you have filled out the MDAC, then you're good for the e-gates!