Tony Vargas
Legend
Niche protection isn't the only way to get to ensemble play and party inter-dependence - or, dare we say it, teamwork. It's just the crudest, most coercive, and most restrictive on players. ;PPlayers tend to want this sort of character, and IMO designers have to fight this desire in order to preserve niche protection and to encourage ensemble or party play. Everyone should have a key thing he-she is good at and a bunch of things he-she isn't so good at, leading to party inter-dependence once they get into the field.
The classic example is the Cleric. If you're looking at the Big 4 classes, you /need/ the fighter to get killed by wandering damage, the thief to get killed by traps, and the Cleric to extend their useful lives by a few CLW spells/day. The Fighter archetype is a clear, familiar, relatable one, and seems tough at a glance, so it's never hard to find players to fill it, you often ended up with two or three (until players figured out they could be an elf fighter/magic-user, anyway). The Thief, likewise, with a bad-boy image, and in leather, no less, you rarely had to push someone into it, there was always at least one guy who wanted to play a thief or a halfling.
Then there was the Cleric, only source of Band-aids, only way to survive huge undead encounters, but not a concept that much appealed. So you had this familiar stereotype of the last player to the table getting stuck playing the Cleric.
The solution is to keep the niches, but lose the protection.
So, in 5e, Clerics - but also Bards and Druids - can be your go-to source of Band-aids for the whole party. (And Turning isn't too OP, so undead encounters are scaled about like any other.) Thieves are the main trap-finders, lock-picks and sneaks, but a Bard with expertise can theoretically match them, and anyone with the Criminal Background can have a go. Fighters are the walking meat-shields, but Barbarians are just as expendable.