But this is a single interface, with two parameters. It's effectively just a function that returns an interface type.

     Graph(N, E)

specialized with

     Graph(int, int)

is roughly equivalent to:

     interface Graph_int_int

ah, that makes sense! but what about something like

    ConvertFromTo(F,T)

? i mean, we need a single method

    func convert(f F) T

but where should it go (which type should implement it)?

The issue there has nothing to do with generics. You need overloading for what you want (and, IMO, overloading is a bad idea). Don't write code that way. Since conversion is rarely a generic pattern anyways, you just pass a conversion function in.

     func processStuff(type U, V)(a U, b V, convert func(U) V){
         bleh(a, convert(b))
     }

     processStuff(123, "foo", strconv.Itoa)

Adding the parts needed to do generic conversion functions is not a great idea. That way lies madness and SFINAE.