Just this one more thing for now… Can I do this?
Thanks.
No - multiple folders, yes, but not multiple collections.
Best,
Keith
Pls consider it a feature request…
Considered, and rejected. 
At least for the foreseeable future. Collections exist on their own - they’re not really intended for viewing together at the moment and there is no interface to do so. But I will certainly consider it when it comes time to plan version 3.0!
Thanks,
Keith
If it is just the data of the collections (the cards) you want to see all at once, remember it is quite easy to create new collections based on existing data. Just select all of the items in Collection A, press the + button to make a new Collection, give it a name, click on Collection B, select all items, and drag them to the new collection.