Porterboxes and alternatives

As you know, Debian projects and sponsor provides so-called "porterbox", but it does not cover all architectures.

There are some alternatives to fix architecture-specific bugs. For the record, let's pick it up them. [1][2][3]

porterbox deb-o-matic qemu
amd64 adayevskaya.d.o debomatic-amd64.d.n DQIB ready
arm64 amdahl.d.o debomatic-arm64.d.n DQIB ready
armel amdahl.d.o abel.d.o debomatic-armel.d.n NG
armhf amdahl.d.o abel.d.o harris.d.o debomatic-armhf.d.n DQIB ready
i386 exodar.d.n debomatic-i386.d.n DQIB ready
mips64el eller.d.o debomatic-mips64el.d.n DQIB ready
mipsel eller.d.o debomatic-mipsel.d.n DQIB ready
ppc64el platti.d.o debomatic-ppc64el.d.n DQIB ready
s390x zelenka.d.o debomatic-s390x.d.n DQIB ready
alpha N/A N/A NG
arc N/A N/A N/A
hppa panama.d.n N/A N/A
ia64 yttrium.d.n N/A N/A
kfreebsd-amd64 lemon.d.n N/A N/A
kfreebsd-i386 lemon.d.n N/A N/A
m68k mitchy.d.n N/A NG
powerpc perotto.d.n debomatic-powerpc.d.n DQIB ready
ppc64 perotto.d.n N/A DQIB ready
riscv64 debian-riscv64-porterbox-01.d.n N/A DQIB ready
sh4 N/A N/A NG
sparc64 kyoto.d.n N/A N/A
x32 N/A N/A N/A

Thus, no alternatives for alpha, arc, sh4 and x32.