Well, we're up past 10 votes now (12: 3/9), and nearly a page of comments, so I'll throw my considerations into the lot:
PRO #1
-For people who want to be able to run stuff over and over and over with all their chars, this offers a lot of replayability to fully gear up your chars.
Counterargument:
-For those of us who don't have the time (or want to spend the time) running things (assuming you can even find a capable team), 1000x, you won't find the gear you want. And, in some cases, gear you NEED to be worthwhile. Case in point: You want to do Fire Lord? You better farm up Searing Gloves, Harness of Fire Protection, and Fire Helm (and Bulwark for Crusader), or essentially 2 of the 3, if you want to tank it. Or else you cannot fulfill your role in the run. Running around with D2-and-lower gear (for those who cannot run D2 1000x with that char) will probably be a suicidal task in D4.
PRO #2
-Stops the powerlevelling of newbies.
No real counter-argument.... It does stop this. But I haven't really seen any of it, myself. Who gives top gear to lowbies in the game just for laughs? Like, D3-quality gear. I've seen it 1-3x, and never on stuff like Poltrooney or Phoenix.
PRO #3
-People ninja loot for alts, and this stops it...?
Umm... It's a weak PRO. Plus, it's easy enough to get them banned from the bot for ninja'ing loot as is, plus just ninja them back when they go to alt out? I dunno....
CON #1
-Finding a team to run stuff with, with their desired characters. I don't know who has a dedicated team to play with, or who can play at set hours, but some of us cannot get this. Likewise, D3 runs required at least 1 tank, and a healer. D4 will likely be the same. If I want to find gear for my Monk, Bard, Sin... (basically, any non Druid, Crus, Zerker, or Bishop), it means someone else has to fill those roles. And what if no-one else wants to fill it? Then the game falls apart. And as much fun as running ogres for money over and over is, it doesn't actually net you very much, in the long run, gear-wise. So, the alternative is that I bite the bullet, as does someone else, and take the necessary roles, while everyone else gets to [potentially, depending on drops] farm gear they want. And then I hope that they all want to come [and have time to come] to the next game to return the favour.
This works if you have a dedicated group of friends who can set time aside for it. Like in WoW guilds and such. This does not work in a public setting, as some poor Bishops and Zerkers are going to get screwed. Over and over. And before you link me to the 2-man D3, or the 5-Bishop D3, remember that they both had fully, 100% geared characters (or very near to it), at top levels, who had already run the dungeon dozens, if not hundreds of times. A new dungeon (D4) will not allow for this from the getgo. And if it does, it's too easy (or so some will say).
CON #2
-The odd time a specific item you need on an alt drops. No-one else needs it. Congratulations, you've just made 400 or 500 gold. Joy.
Don't laugh; it happens. It happens now, courtesy of the 2-load limit. But it would happen a lot more if you couldn't alt any gear at all.
I truly do not want this to devolve into a flame war (it doesn't look like it has, yet, but I want to warn people in advance). However, my opinion is that this change is good for one group: Those with lots of dedicated time and friends in this game. Everyone else will suffer, and fall horribly behind those who have those requirements met.
I play Gaia's whenever I can, and yet I still have yet to get a single fully-geared D3 char. Part of this comes from me playing a single role (Bishop) a lot, because it's needed. Part comes from me getting unlucky rolls on drops (I have yet to win a Demon Heart.... 0/5). So it's not like I'm griping while fully outfitted; I try very hard to kit my characters, with the current system, and I run it as frequently as I can, but I am still woefully behind. Not to mention, I have so little Sin/Hunter gear it's funny, meaning these 2 very-gear-dependant classes are pretty much useless in team play, as is.
I'm aware that you're in the "it's not up for debate" rationale, Zwieb, but I truly do believe that this implementation will simply divide the Map up so much so that only the dedicated, hardcore fans (a mere fraction of those who can play, now), will continue playing. Because they will have the friends to help them run gear for alts, and who can return the favours of running necessary-classes in the Dungeons. For the rest of us.... well, I wouldn't make a healer or tank again, given the chance, because if I had it I'd be forced to use it. Instead, I'd get to leech off of a few dedicated folks who are forced to either play those roles, or create a new game to find others who can fill these roles.
Once again, this is not a flaming match. This is an exchange of opinions. Please be respectful of others' while you provide your own. You can debate, but trolling and flaming is not appreciated, nor permitted.