If we are talking about official releases...the Nexus should be the first (with or without GPE).
If we are talking about leaks....there is more chance of appearance on GPE phones.
At least, the last year when the S4 GPE arrived...the 4.3 leaked ROM arrived much sooner than the 4.3 Nexus 4 leaked ROM. (Yes, there was a leaked system dump from a test Nexus 4 with 4.3).
Nexus 5 (Stock + Franco Kernel) - Galaxy Nexus (CM11 + A.S.K.P. Kernel) - Nexus 7 2012 (Stock); Galaxy S GT-i9000 (CM11 - zRAM OFF); Galaxy Y Pro B5510L (Stock).
Nexus 4 16GB; Galaxy S3 GT-i9300.