I speak often of 'The Vastness' so it might be a good idea for me to tell you what it is. But I really have no idea.
Though there is probably a justifiable time to speak of 'the' Vastness, it might be better to start by speaking of 'a' vastness. This is a vastness among many others whereas The Vastness assumes one Vastness, which, of course, is what Vastness must most certainly be. Yet vastness is, in the end, an entirely individual, psychological experience; it is another thing altogether to speak of a universal Vastness.
There is an almost overwhelming desire to objectify reality, and yet our every experience of reality is a completely subjective one. Many objective universals suggest themselves, yet ultimately they are all rooted in subjective experience.
I honestly don't know whether what I have said here is a 'heterodox view' or not, though I suspect that it is. I suspect a Zen master would tell me I can experience The Vastness, an objective realization of the Ultimate. Who am I to quibble? My only question would be whether or not it is necessary to begin with the presupposition of the Objective Universal. And here I think he would answer in the negative.
One experiences a vastness, and upon experiencing it, is free to come to one's own conclusions about its universal objectivity. So, although it may all come down to the chicken versus egg absurdity, as individuals we are in possession of only the egg. And we can, if we wish, sit on this egg and see what hatches. If and when it does, these distinctions will likely have no meaning at all.
This may seem like just a lot of word play; and certainly some of it is. But there is also something of importance (to my thinking) that is being said. The path of not-knowing leads directly to one's inner, subjective experience. And that experience forever empties itself of objectification; this is how it remains open. This is that 'critical zero-ing' discussed (seemingly) so long ago. If Vastness is empty, then any and every objective truth is clutter and other than that experience of vastness.
This is but one approach among as many as there are those who wish to have one. For all I know, bhakti yoga, the path of devotion to a single objectification of reality is as effective as any other. Only, if that way is to be effective, then that is what the practitioner must necessarily wholeheartedly do. And this similarly applies to a path of not-knowing. Thus I explain my apparent dogmatism.
I'll close with a repetition of maxim 67.3: "You don't have to get it 'right' to get it." Only you have to get on with getting it.
You can check out Scott's other miscellaneous writings here.