So today I picked up a TP-Link Archer D5 V1.0 for $5, I can confirm that OpenWRT works on this device by following the same instructions as the Archer D7.
Same caveats apply, there is no dsl modem and the lights don't work properly (it also shows as model Archer D7 in system info).
The uart headers are in about the same spot on the board (and in the same order).
MTD Layout:
[ 0.494900] Creating 7 MTD partitions on "spi0.0":
[ 0.499779] 0x000000000000-0x000000020000 : "u-boot"
[ 0.505620] 0x000000020000-0x000000fb0000 : "firmware"
[ 0.513369] 2 tplink-fw partitions found on MTD device firmware
[ 0.519376] Creating 2 MTD partitions on "firmware":
[ 0.524459] 0x000000000000-0x000000104b5e : "kernel"
[ 0.530329] 0x000000120000-0x000000f90000 : "rootfs"
[ 0.536064] mtd: device 3 (rootfs) set to be root filesystem
[ 0.543376] 1 squashfs-split partitions found on MTD device rootfs
[ 0.549700] 0x000000680000-0x000000f90000 : "rootfs_data"
[ 0.555960] 0x000000fb0000-0x000000fc0000 : "radioDECT"
[ 0.562114] 0x000000fc0000-0x000000fd0000 : "config"
[ 0.567909] 0x000000fd0000-0x000000fe0000 : "romfs"
[ 0.573677] 0x000000fe0000-0x000000ff0000 : "rom"
[ 0.579235] 0x000000ff0000-0x000001000000 : "art"