Well there's different possibilities as you probably already thought.
You could just add ADCs and Supports to the threat list or create a second rune pages. In the first you'd list ADCs and in the second you could rank Supports. However with the second suggestion you'd have to somehow point out for readers that there's a second list.
I've also seen writers listing all the champions they wanted and created a special chapter for synergies and counters. The champions had either a pretty small explanation text or had all the same saying that there was a particular chapter that focused on counters and synergies. :) Those chapters are usually located after game phases (early/mid/late) or before those because it's always nice to know how to play with a Jhin as marksman against a Lucian with a Bard support. And then you can dive into laning phase etc.

Haha, I'm secretly waiting for a new tanky support that's flabberghasting. But none so far in sight! It really depends on what kind of champion you like to play. Like if you prefer rather tanky ones, try Leona and Braum, maybe Blitzcrank and Nautilus.
But if you're one that likes Crowd Control, go for Janna, Lulu, Brand, even Veigar would be interesting. Safe picks like Soraka can look boring at first, but they're actually most of the time the game makers, Thresh and Blitzcrank too, btw. :)

I hope I could at least help you a little. Or maybe you've come up with your very own idea already.

Cheers, Wicked Cherry.

Okay cool, if you want, give a short message when you've updated them and I'll share my feedback and thoughts about it. :]