is there an announced reason why corki's base damage nerf was reverted? like they changed their mind and corki doesn't need a nerf or are they planning on something bigger nerf or even a mini-rework for him on next patch 7.24B
Nothing announced so far - sometimes Riot employees provide context around changes when they revert them, but they haven't said anything about Corki this time around.
Personally, I doubt it points towards a mini-rework. It's more likely that those changes took Corki a little too far in the wrong direction (remember everything's still being tweaked around Runes). Might be that later patches bring the same changes back, or transfer them to somewhere else in his kit.
Yup, got reverted in last PBE patch. Could return but unlikely.