Carrier bloatware apps are quite an issue in the US, where many smartphones ship with almost as much useless junk as they do genuinely necessary applications. This junk is lovingly called "crapware," "bloatware," or "shit" interchangeably by those in the smartphone community. Because it is. This disdain largely stems from the fact that many bloatware apps can't be fully uninstalled, only disabled (some can't even manage to do that).
In Android 5.0, Google is hoping to give everyone another option: don't be so awful about it. In Lollipop, carriers can have a list of applications downloaded to a device automatically on first boot through the Play Store, meaning those apps are installed on the data partition, not the system one. System partition apps can't be removed without root permissions, but those on the data partition can. The point of this, obviously, is to let users know that they actually can get rid of all the useless junk carriers put on their phones.
Of course, the key question is whether or not carriers will actually make use of this new feature. Ron Amadeo's interview with Google over at Ars Technica doesn't make this clear. And in all honesty, it seems more than likely that many carriers will take a pass on this, because they don't want users to be unable to uninstall bloatware, because that decreases its value as an advertising placement tool.
Still, it's very cool that the option now exists, and hopefully we'll see it in action on the upcoming Nexus 6.