We actually get this suggestion pretty regularly. It was something we considered and very nearly included. We haven't reconsidered it recently but I could see it being a discussion topic again.
It has the advantage of convenience when navigating very large timelines. It also would probably help once we end up with more types too. Right now, I'd personally be more interested in a filter style. Something like a collapsible list of toggles you could select which types to highlight. That way you aren't wondering if you've used the right search term. Many people who played a lot of D3 would search "legendary" hoping to find "uniques" and get nothing as a result.