[Xperia Z5 Android Development] militiaOfDeath:
Compared the content of xposed installers for sdk23 and sdk25, and it seems to only be one additional file in the sdk25 installer, /system/lib64/libart-compiler.so. Tried modifying the part in the rootkernel.sh that handles the Xposed installation to (see outlined in bold)

add_xposed()
{
local file
local LIBDIR
local install
local pattern
local XPOSED
local XPOSED_DIR=xposed

[ $PLATFORM -eq 64 ] && pattern=xposed-*sdk${SDK}-arm64.zip || pattern=xposed-*sdk${SDK}-arm.zip

for file in $pattern; do XPOSED=$file; done
[ ! -f $XPOSED ] && return

if [ "${VERSION%%.*}" != "7" ]; then
ui_print " Skipping xposed integration. Only supported for Android 7"
return
fi

ask "- Found $XPOSED. Install?" 1 install
[ $install -ne 1 ] && return

perform rm -rf $XPOSED_DIR
perform mkdir -p $XPOSED_DIR
unzip_with_timestamp $XPOSED $XPOSED_DIR

add_vendor_overlay

local policy=$(find_file $RAMDISK/sepolicy)
se_allow ${policy} dex2oat	apk_tmp_file	dir	search
#	Avoid the LD_PRELOAD is removed on transition from installd to dex2oat
se_allow ${policy} installd	dex2oat	process	noatsecure
se_allow ${policy} untrusted_app	dex2oat	process	noatsecure

perform mkdir -p $RAMDISK/$VENDOR_OVL/framework
perform cp $XPOSED_DIR/system/framework/XposedBridge.jar	$RAMDISK/$VENDOR_OVL/framework/XposedBridge.jar@0644
perform cp $XPOSED_DIR/system/xposed.prop	$RAMDISK/$VENDOR_OVL/xposed.prop@0644
add_with_xz $XPOSED_DIR/system/lib/libart.so	$RAMDISK/$VENDOR_OVL/lib/libart.so
add_with_xz $XPOSED_DIR/system/lib/libart-compiler.so	$RAMDISK/$VENDOR_OVL/lib/libart-compiler.so
perform cp $XPOSED_DIR/system/lib/libsigchain.so	$RAMDISK/$VENDOR_OVL/lib/libsigchain.so@0644
perform cp $XPOSED_DIR/system/lib/libxposed_art.so	$RAMDISK/$VENDOR_OVL/lib/libxposed_art.so@0644
perform cp $TOOLS/libxposed_preload32.so	$RAMDISK/$VENDOR_OVL/lib/libxposed_preload.so@0644
perform cp $TOOLS/libxposed32.so	$RAMDISK/$VENDOR_OVL/lib/libxposed.so@0644
perform cp $TOOLS/libxposed_safemap32.so	$RAMDISK/$VENDOR_OVL/lib/libxposed_safemap.so@0644

if [ $PLATFORM -ne 64 ]; then
perform cp $XPOSED_DIR/system/lib/libart-disassembler.so	$RAMDISK/$VENDOR_OVL/lib/libart-disassembler.so@0644
else
perform cp $XPOSED_DIR/system/lib64/libart-disassembler.so	$RAMDISK/$VENDOR_OVL/lib64/libart-disassembler.so@0644
add_with_xz $XPOSED_DIR/system/lib64/libart.so	$RAMDISK/$VENDOR_OVL/lib64/libart.so
[COLOR="Red"][B]add_with_xz $XPOSED_DIR/system/lib64/libart-compiler.so	$RAMDISK/$VENDOR_OVL/lib64/libart-compiler.so[/B][/COLOR]
perform cp $XPOSED_DIR/system/lib64/libsigchain.so	$RAMDISK/$VENDOR_OVL/lib64/libsigchain.so@0644
perform cp $XPOSED_DIR/system/lib64/libxposed_art.so	$RAMDISK/$VENDOR_OVL/lib64/libxposed_art.so@0644
perform cp $TOOLS/libxposed_preload64.so	$RAMDISK/$VENDOR_OVL/lib64/libxposed_preload.so@0644
perform cp $TOOLS/libxposed64.so	$RAMDISK/$VENDOR_OVL/lib64/libxposed.so@0644
perform cp $TOOLS/libxposed_safemap64.so	$RAMDISK/$VENDOR_OVL/lib64/libxposed_safemap.so@0644
fi
add_preload libxposed_preload.so

perform rm -rf $XPOSED_DIR
}

But that didn't work (bootloop after Android logo), so must probably do some more changes I assume. If anyone has any suggestions, yell out. Would be cool to be able to get Xposed integrated into the boot.img.