Sony Xperia Z2 Tablet WiFi (castor-windy)
The z2 tablet would probably a good choice device for replicant as.
Uses qcom soc without a modem,.
Has full graphics acceleration via freedreno on android
It's quite new.
Works nice with the mainline Linux kernel.
I currently have a working aosp 8 using linaros generic_device tree only needing 3 firmware files (WiFi (in Linux firmware) + GPU) it is graphics accelerated using freedreno and although WiFi isn't working yet it should be easy to fix, trying to get iommu working first though.
Sorry for not responding to this a long time ago, but this device actually sounds very interesting. Do you happen to know if it can run a free software bootloader like u-boot as well? Have you made any more progress on it that hasn't been upstreamed yet? I noticed this: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/arch/arm/boot/dts/qcom-msm8974-sony-xperia-castor.dts