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.