Suggesting that future support will be dependent on someone taking up the task of porting the device to ath79.
Build appears good on reasonably current master
jeff@deb-devel:~/devel/openwrt$ git log --pretty=oneline -1
62940df3a9 (HEAD -> master, openwrt/master, openwrt/HEAD) procd: update to latest git HEAD
jeff@deb-devel:~/devel/openwrt$ ./scripts/diffconfig.sh | egrep -v '^#'
CONFIG_TARGET_ar71xx=y
CONFIG_TARGET_ar71xx_generic=y
CONFIG_TARGET_ar71xx_generic_DEVICE_archer-c60-v2=y
CONFIG_DEVEL=y
CONFIG_CCACHE=y
jeff@deb-devel:~/devel/openwrt$ ls -l bin/targets/ar71xx/generic/
total 22330
-rw-r--r-- 1 jeff jeff 7918 May 29 11:32 config.seed
-rw-r--r-- 1 jeff jeff 4288853 May 29 11:34 openwrt-ar71xx-generic-archer-c60-v2-squashfs-factory.bin
-rw-r--r-- 1 jeff jeff 4260614 May 29 11:34 openwrt-ar71xx-generic-archer-c60-v2-squashfs-sysupgrade.bin
-rw-r--r-- 1 jeff jeff 2294 May 29 11:34 openwrt-ar71xx-generic-device-archer-c60-v2.manifest
-rw-r--r-- 1 jeff jeff 3014656 May 29 11:34 openwrt-ar71xx-generic-root.squashfs
-rw-r--r-- 1 jeff jeff 1592969 May 29 11:34 openwrt-ar71xx-generic-uImage-lzma.bin
-rwxr-xr-x 1 jeff jeff 5122940 May 29 11:34 openwrt-ar71xx-generic-vmlinux.bin
-rwxr-xr-x 1 jeff jeff 5128064 May 29 11:34 openwrt-ar71xx-generic-vmlinux.elf
-rw-r--r-- 1 jeff jeff 1638400 May 29 11:34 openwrt-ar71xx-generic-vmlinux.lzma
-rwxr-xr-x 1 jeff jeff 1603092 May 29 11:34 openwrt-ar71xx-generic-vmlinux-lzma.elf
drwxr-xr-x 2 jeff jeff 48 May 29 11:34 packages
-rw-r--r-- 1 jeff jeff 1066 May 29 11:35 sha256sums
There is likely something wrong with your build system or configuration as it builds openwrt-ar71xx-generic-archer-c60-v2-squashfs-factory.bin without issue from current master.
Most robust would be starting with a fresh clone.
You can try to track it down by increasing the log verbosity with
The most likely reason would be the build config just being too large, given that there will always be some devices on which the currently release images won't fit anymore, the buildsystem just skips over them (although you will see complaining about it in the build logs). So give jeff's minimal build config a try first (I'm not suggesting to actually flash it, if you're in need of additional features, like e.g. luci, just to test building a known working minimal config for testing).