gistfile1.cs

using System;

unsafe struct S
{
    public void* ptr;
    public object obj; 

    static void Main()
    {
        S s = default(S);
        Console.WriteLine(Equals(s, s));
    }
}

Interesting, why struct with only one pointer or with pointer and value type behaves correctly?

using System;

unsafe struct S_Ok1
{
    public void* ptr;
    public void* ptr2;
}

unsafe struct S_Ok2
{
    public int n;
    public int* ptr;
}

unsafe struct S
{
    // Could be any reference type
    public object o;
    public int* ptr;
}
class Program
{
    public static void Main()
    {
        S s = default(S);
        S_Ok1 sOk1 = default(S_Ok1);
        S_Ok2 sOk2 = default(S_Ok2);

        Console.WriteLine(Equals(s, s)); // False
        Console.WriteLine(Equals(sOk1, sOk1)); // True
        Console.WriteLine(Equals(sOk2, sOk2)); // True
    }
}

I assume that you ideas is correct, but in case when struct doesn't contains reference type fast version of Equals method is used:

// Inside ValueType.cs
bool Equals(object obj)
{
    //Compare type 

    object a = this;
    if (CanCompareBits(this))
    {
        return FastEqualsCheck(a, obj);
    } 

    //Compare using reflection
}

It seems that CanCompareBits return true only when struct contains reference type but returns true if struct contains unsafe pointer, and this comment from Rotor is not accurate:

The comment of CanCompareBits says "Return true if the valuetype does not contain pointer and is tightly packed". And FastEqualsCheck uses "memcmp" to speed up the comparison.