the fone is nearly identical to the supported Z5 sumire.
It would be less effort and double advantage
I don’t think there is much chance of ivy becoming an officially supported device: /e/ is built on LineageOS and LOS support for ivy stopped at Nougat (Android 7). LOS and /e/ support for sumire also stopped at Nougat, and I don’t think /e/ want to add any more Nougat devices.
If you want to try installing /e/ on your Z3+, I have recently made unofficial ‘v-0.14-nougat’ builds for the Sony devices which are stuck on Nougat. I plan to continue making these builds whenever /e/ gets a version upgrade (so the next will be ‘v-0.15-nougat’, sometime in February or March I guess).
You can find the builds from the following post: