Problem: allReady() could try and detect relevant subscriptions

[janat08]

Problem: When you navigate to page and swiftly return back to previous page it will be loading even if it's actually not if you just used allReady() everywhere as we did.

Solution: Either assume that all of the subscriptions are used in tracker and detect if there's a tracker depending on subscription or assume that allReady() is used in a blaze spacebar's {{else}} condition in a list's {{#each}} therefore possibly having Template.currentData() serve as reliable source of whether a subscription is being used (which would be flimsy way to render things even in our case).