Well, I may have found it... my holy grail of bags (for now, anyway). The Landscape Satchel by Tanner Goods. I don't have one in my hand as they are made to order. And the price is a little... over the top end, for me anyway (especially as I saw a women with a really nice leather messenger bag after a gallery opening the other day and it cost her all of - $70.00).
Anyway, I like the look of this one - in all three colours actually. Black would definitely be my first choice though, followed by brown. I also like the idea of the removable zippered insert - pouches for this and that or just a big empty bag.