Thinking to build a portable pc to replace my laptop I rarely use as a laptop. I can’t get past the matx itx case decision. It seems to me there are better itx cases available for portability that will handle a massive GPU. Thoughts on matx vs itx builds.
mATX is kinda in a tricky spot. On the one hand, you have the form factor that makes a sandwich case impractical. On the other hand, it should be possible to create a sub-15 liter case without much extra work.
I would recommend one of two options here, either the Sliger Cerberus or the SFFTime P-ATX / N-ATX:
Sliger is more robust and possibly more available in the U.S, SFFTime has longer lead times but allows for super-slim builds 
If you’re ok with ~22L as “SFF,” the SAMA IM01 is a great little MATX case with a lot of flexibility. You can even use either ATX or SFX PSUs, although if you want a long GPU you do have to go with SFX or a much shorter CPU cooler.