That's a great idea! What I loved about these cards was their flexibility. I feel honored that this method struck a chord with you because there are some wonderful suggestions that have come forth. For me, this was one of those things that, in retrospect, I would have used more extensively.
My dd graduated and I had loaned her timeline book to a dear friend. When my friend recently returned it, my first impression was how much empty space there was in the timeline. My second impression was how creative those little picture cards were; my dd had used richly colored markers for most of them. They brought back good memories.
You can always add the cards to a book timeline later if you ever feel that you must do a timeline. We actually didn't glue the cards in, but just slid them into picture protectors in the proper place. They would probably make great scrapbooking material as well.
One more thing: these cards store well in an index card holder (you can get the long holders if you accumulate a lot of cards). I used index card dividers (like for a recipe box), and labeled them with dates every 500 to 1000 years for BC and then closer increments for AD dates. It makes them easier to store and find them as you progress. Hope this is clear. Have fun!