Go is a compiled language, which means that every function must exist beforehand; because of this, the only way an application author can create a helper function, is to add it to the REI3 source code. Or have us add it for them. This would be very limiting and also unnecessary as we already have 2 languages that application authors can use to create helper functions. Adding Go would not solve a problem - and I say that as someone who loves Go.
If you need a helper function on the frontend, you should create a frontend-function - calling pre-defined Go code on the backend would usually be slower as you´d have the latency of exchanging data with the server.