cooling door

I can lease 10 racks,
put T1600s in two of them, and leave the other 8 empty; but
that hasn't helped either me the customer or the exchange
point provider; they've had to burn more real estate for empty
racks that can never be filled

Seems fine to me, you used your power in two racks, to get more power
will cost the provider more so you will have to pay more. This is just
an extreme example of blade servers causing half a rack to be empty
the facts haven't changed no matter how bad seeing empty racks feels

Waste implies you could use it for no additional cost, old pricing
models were vulnerable to gaming on combinations they'd not thought

It might be easier for people to understand in these cases
if the provider put yellow/black stripe tape over the unused
space with a big sign saying "not yours"

I'm paying for floor space in my
cage that I'm probably going to end up using for storage rather
than just have it go to waste

That's nice, I hate cages where you have no room for tools or to work
and the kit hits the walls when you try and unrack it. I've no
idea how they fit a normal engineer in some

and we still have the problem of
two very hot spots that need relatively 'point' cooling solutions.

Accepted, big fan on the back of the rack? Plenty of empty
space for such solutions.

High density servers seem to be vendor driven, they can
charge more and make you buy the switch and other ancillaries
you'd likely choose cheaper from others. And when new models come
out the whole lot gets replaced rather than just the odd few U
of servers. The convenience may be worth the high price for some

Density is just another DC design parameter to be optimised for