PHP trivially scales up to multiple nodes behind an LB. You're really only limited by your backend storage connection count and throughput.
Go and friends may make for more efficient resource utilization, but it will be marginal in the grand scheme of things unless there are plans to do massively different things.
As it is this code is very simple. I haven't used PHP in 15 years and I was able to trace through this from front-end to back-end in less than 3 minutes.
To me it look like a really great level of complexity for the problem it solves.
Go and friends may make for more efficient resource utilization, but it will be marginal in the grand scheme of things unless there are plans to do massively different things.
As it is this code is very simple. I haven't used PHP in 15 years and I was able to trace through this from front-end to back-end in less than 3 minutes.
To me it look like a really great level of complexity for the problem it solves.
Keep it up, OP.