There are more powerful ARM SBC boards out there.
Take a look at Pine64.org for example. They have a Rock64 board that supports up to 4 gig of RAM with quad core CPUs. They are under $50.
I personally would like to see an ARM competitor to the Intel NUC. 4GB and 4 cores sounds great but might not be enough for development or certain benchmarks. Something like 16GB RAM and at least 8 fast cores with a fast SSD should be enough. It seems that you can only get ~50$ devices or >2000$ servers (if they even sell single ones). I guess we have to wait for Apple to sell a MacBook with their own cpu.