I hope that wasn't the actual reason why they decided against a REPL or other tools, because unfortunately, most of us aren't as smart as Ken.
That said, a REPL would be nice. Seems like go compiles fast enough that some ambitious dork could make a REPL-faker?
Languages that have a REPL were engineered from the start to allow it. Go doesn't do late binding so much. It prioritized a higher degree of control over low level memory layout and substituted fast compiling for a REPL.