I’m curious because now it’s seems like there are 3 solutions. Although I really like the simplicity of this solution and the modernizing from the constraints of true classic mode.
If you can run within the standard environment, I'd suggest you do (but you should check pricing, etc to see if it suits). Especially if you want 0-1 scaling.
I migrated golang.org from standard to flexible a couple weeks ago, primarily because of increased control over the runtime (custom Docker image) and increased instance sizes (configurable memory, CPU past the App Engine limits, which caps out at 2 GB). See https://golang.org/issues/27205 if you want to read more.
It currently runs on two fat flexible instances (GCE VM), but could easily run on one. We only run on two for some redundancy.
I've measured throughput of ~thousands of requests per second on a F4_1G on apps I've worked on previously. They were CPU-constrained, but not doing very much (JSON serialization).
The new runtime might be even better, since GOMAXPROCS is no longer 1.
correction to my post above: 1 GB is the max memory for standard: https://cloud.google.com/appengine/docs/standard/#instance_c...
So two of the solutions are flex and go1.11 on standard. Is the third solution the older runtime versions (eg 1.9 and earlier)? If so, then there's really just two solutions, since 1.11 replaces 1.9 on standard.