Yeah my knowledge/experience with the TPL is pretty much non-existent!
But, I do think what you are suggesting is what I am currently doing in u-boot. I am deferring the programming of the core until I am within u-boot i.e more suitable for faster programming (and can handle loading bigger files, such as the core .itb, from an EXT4 partition). The SPL doesn’t seem to be able to successfully load files any bigger than ~300-400KB from an EXT4 partition. This is not an issue if the SPL is loading bigger files from FAT, the support seems to be there. Hence the reason for this thread, just to see if anyone else had tried this.
However, as we discussed in your thread (Arria10 u-Boot 2021.04 support reboot from linux - #3 by mawillia), I am actually quite happy with the SPL loading the peripheral, and u-boot loading the core, as it is more efficient.
Thanks,
-RD