The question is in the subject line, but why do we restrict ourselves to small (potentially tiny) system image by preserving the (apparently unused) radio calibration data partition and the (apparently redundant) copy of the PLC firmware partitions? I could use the space...
NB. I have a TL-WPA8630P(UK) V2.0 with firmware 2.0.2 Build 20170509 Rel.58359 on it. As I mentioned elsewhere it turns out I could flash it with TP-Link's EU V2.0 firmware 2.0.3 Build 20171018 Rel.36564, which made me think it was similar enough to try flashing OpenWrt with a v2.0-eu factory image. If anyone wants an image of the 2.0.2 Build 20170509 Rel.58359, tell me how and I'll send it, before I flash my second unit over to OpenWrt.
Yes, that unused 1MiB PLC space is such a waste. It would have been great for OpenWrt if TP-Link had put it beside the rootfs (or better yet inside the rootfs). You can see there is a mix of device-specific and settings partitions alongside the different firmware partitions, which must have been a headache for them to handle when rolling out firmware updates. But we should still be thankful to them for being able to run it at all in this age of locked down hardware
I updated the partition explanation in the Wiki here.
If you want to test the "unofficial BETA" ath79-tiny build with LuCi + 1MB free space, see this comment