Inbox by Gmail has 2 killer feature: snoozing messages to a later date and bundling, i.e. grouping messages by label in the inbox,
As far as I understand bundling brings three limitations.
You cannot give more than one label to a message, what has long been a distinctive Gmail feature. This makes some sense in the inbox, because grouping can happen only by one given label, but not when you archive messages (now you mark them as "done").
You cannot manually label messages in the inbox (without a label automatic filtering rule). Now I understand that, if the idea is to group inbox labelled items, labels not intended for bundling are moved from the inbox. But why bundling labels require an automatic filter, why they can't be assigned manually to messages is something I don't get and don't want.
Finally (perhaps to discourage manual bundling), there are no shortcut facilities to select the desired label.
As for manual bundling there is a workaround. In fact despite you need an automatic filter, you can still bundle manually other messages not matching it.
Given this, I create a never matching filter, say mail from email@example.com
Since there is a an automatic filter, this can be declared as a bundle and I can manually attribute the bundling label to messages as desired.
As for multiple labels I don't know how to workaround the limitations, and the same is for label autocompletion.
If you have some workarounds, please help.