A refinement of the half-baked idea

module-generic-init-multi.go

/* define generic package */

// file p.go
package p
typevar K generic.ComparableType  // poor man catagory
typevar V generic.AnyType         // ^^

import (...)

type X struct {
   k K
   v V
}

func (p *X) Get() (K, V) { return p.k, p.v }

// -----------

/* use generic package - module type directive decl. can be done various way */
package main

/* possible way for having n distinct type flavors of a given gen package in same source */

import (
    psb "p" //+build {K:string, V:[]byte}
    pss "p" //+build {K:string, V:string} 
)

func main() {
    var x = psb.X {"this-thing", []byte("it is generic"),}

    var k string
    var v []byte
    k, v = x.Get()

    var x1 = pss.X {"this-thing", "it is generic",}

    var k1, v1 string
    k1, v1 = x1.Get()

} /* the Q is how far does this get us .. */

Sans the hypothetical generics package (magic package ala builtin), this is mostly the build tool chain, so yes, code generation.