Ok. I've been dancing around this, but I might as well just be clear:
The reason I am reticent to add a "CBM DOS compatibility mode" is because I don't want to either make a "competing product" or be able to be accused of making a "competing product." I initially entertained the idea of a compatibility mode because it was theoretically possible, but now I'm backing away from even the possibility.
If someone came to me and said "Hey! I'm really into the CBM DOS they had in the C64 back in the day, but I want a newer computer, perhaps with better graphics. What would you recommend?" I would steer them right to the x16 if they thought the VERA was cool, or if not, another CBM DOS compatible computer (Which I won't name, as that would be advertising for a competing product.)