I'm not sure it's anywhere near as bad as some people keep suggesting. Firstly, how many enclosures do you really need to replace what you currently have internally? I have five drives inside my current Mac Pro, and there are definitely enclosures that can fit all that; expensive yes, but not so much so that buying lots of smaller enclosures would be cheaper. Thunderbolt can easily provide the bandwidth needed for that many drives. It's also possible to use USB3 depending on your exact needs, but it's not really recommended unless you can find an affordable USB3 enclosure with hardware RAID (as USB doesn't handle multiple drives over a single connection very well), but most of those approach Thunderbolt enclosure prices anyway.
The other thing people don't seem to be thinking about is; you don't have to put those enclosures right next to the new Mac Pro. Some computer desks come with a shelf underneath for hiding away drives, routers etc., or you can put them an under-desk cupboard (though you should get one with space for air to flow).
Not saying the cable clutter isn't regrettable; I just recently moved a desk used by my family for two computers, and had to handle all the cabling for that, which is a pain to do neatly, and I think had a total of 11 power connectors, four of which were power bricks, and 3 of which were plug-in adaptors (of which one was ridiculously huge). That's covering one Time Machine drive each, the machines themselves, monitor for the Mac Mini, a pair of external speakers each, a printer, a scanner, a switch for my wired network and I don't even remember what else.
To be honest I'm not sure a new Mac Pro is really that much worse than the detritus you can accumulate for any machine, plus for professionals an external enclosure has been necessary for bulk storage anyway; the main issue there is that many existing enclosures are Mini-SAS or eSATA, neither of which is directly compatible with the new Mac Pro.
but I guess that would be asking too much now...
