OK. I did a test build for arm64 and it builds fine. Debian should default to building all arches unless there is a good reason why it won't work. So far as I am aware there is no particular reason to restrict this package to x86, even if that's all upstream cares about.
The attached patch enables it for all architectures. We can review failures if they are any once it is uploaded, and perhaps restrict it to a specific set of arches if need be. I am happy to NMU this minor fix if the maintainer is busy. Wookey -- Principal hats: Linaro, Debian, Wookware, ARM http://wookware.org/
diff -Nru spice-0.12.8/debian/changelog spice-0.12.8/debian/changelog
--- spice-0.12.8/debian/changelog 2016-07-26 03:07:46.000000000 +0000
+++ spice-0.12.8/debian/changelog 2016-12-07 00:31:25.000000000 +0000
@@ -1,3 +1,10 @@
+spice (0.12.8-1.1) UNRELEASED; urgency=medium
+
+ * Non-maintainer upload.
+ * Enable more architectures than just x86
+
+ -- Wookey <woo...@debian.org> Wed, 07 Dec 2016 00:31:25 +0000
+
spice (0.12.8-1) unstable; urgency=medium
* New upstream release
diff -Nru spice-0.12.8/debian/control spice-0.12.8/debian/control
--- spice-0.12.8/debian/control 2016-07-26 03:00:47.000000000 +0000
+++ spice-0.12.8/debian/control 2016-12-07 00:20:58.000000000 +0000
@@ -23,7 +23,7 @@
Package: libspice-server1
Section: libs
-Architecture: i386 amd64
+Architecture: any
Multi-Arch: same
Pre-Depends: ${misc:Pre-Depends}
Depends: ${shlibs:Depends}, ${misc:Depends}
@@ -42,7 +42,7 @@
Package: libspice-server1-dbg
Section: debug
-Architecture: i386 amd64
+Architecture: any
Priority: extra
Multi-Arch: same
Pre-Depends: ${misc:Pre-Depends}
@@ -59,7 +59,7 @@
Package: libspice-server-dev
Section: libdevel
-Architecture: i386 amd64
+Architecture: any
Depends: libspice-server1 (= ${binary:Version}), ${misc:Depends}, libspice-protocol-dev (>= 0.12.10~)
Suggests: pkg-config
Description: Header files and development documentation for spice-server
signature.asc
Description: Digital signature
