IMO, siloing is absolutely a good thing. In fact, I think we could use a bit more of it. The only drawback I see to siloing is that it leads to more complicated chargen systems.
Very rarely have I seen a specialized noncombat character work out well in play. IMO, a player experienced and savvy enough to make such a character work is a player experienced and savvy enough to sit down with the DM and work out a house-ruled solution.
(And of course there's the flip side, which is characters specialized for nothing but combat, which siloing also prevents. I'm somewhat amused that those haven't come up yet.)
One thing I do think D&D could use, however, is characters whose combat abilities manifest through henchmen or other PCs - the warlord has a little of this going on, but I'd like a class built around it. Such a class would allow the creation of characters who were "noncombatants" in the strict sense, while still being able to contribute when the crap hits the ventilator.
For those who've played the solo adventure WotC put out a few days ago, Splug is a good example of this sort of thing (albeit a highly simplified one). He's your cowardly goblin buddy whose usual combat move is an ability called "Cringe," wherein he cowers and whines and keeps the enemy's attention, enabling you, the boss, to get an extra attack. It's a nice way of giving you a mostly noncombat lackey who can "pull his weight" in a fight.