It seems silly that when you open an InDesign document and it uses TypeKit fonts that aren't available, there is no direct link to take you to the website and fix this.

Firstly, it should just automatically activate the fonts if they're in TypeKit and you haven't already hit your limit.

Secondly, if for some reason this behaviour is undesirable, you should be able to activate them from within InDesign. The process for new/occasional users is actually quite hard: a vague mention of the Creative Cloud app is all you get. Many users don't know what that is. Then you have to know to go to the "Assets" tab, then the "Fonts" tab, then press "Manage fonts", which takes you to a website, where most of the time I find you're not signed in, so you have to sign in, and THEN you're shown a list of the fonts you have synced... by now, assuming they have managed to wend their way through that, my users are saying "now what do I do?"

How about in the "Find Fonts" dialog there is a button marked "TypeKit". In that it displays a list of all fonts available in TypeKit with a checkbox next to each. Sort of like the old ATM Deluxe or Suitcase.