I'm curious, because I think the Mill as described in the talks is vulnerable to a variant of Spectre. If you have a sequence of code like this:

    if (index < bounds) {
        index2 = array1[index];
        ... array2[index2];
    }

If the compiler speculates both array accesses above the bounds check, then the first one can still succeed (i.e. not produce a NaR) while accessing attacker-controlled memory for the value of index2.

You could obviously fix this by never generating code that does double speculation, but you could also do that by modifying a conventional OoO microarchitecture.