This post is about search tabs and lenses. I'll motivate my feature suggestion primarily with lenses but touch on the general theme towards the end.
I really like that lenses are a feature. Currently, I like to use them when a default search turns out to not be specific enough and I want to tailor results further.
Many of the default Lenses are clearly meant for exploration rather than tailoring results, e.g. small web. What is unfortunate then is that a lens must be manually activated, and that you have to manually choose one from a drop down. This design renders using lenses a highly deliberate act, because it introduces a considerable amount of cognitive friction. In other words, getting into the habit of using Lenses is harder than it has to be.
So the idea then is to reduce the amount of cognitive friction for using Lenses. One idea that came to mind is to be able to have lenses as UI tabs in the search much like Images and Maps. This seems like a small change, but not having to toggle on/off and go through the drop down would make it significantly easier to make use of on the fly.
Perhaps the user can select up to X lenses to show as tabs with the rest remaining in the overflow/dropdown menu. Perhaps this feature also implies being able to modify the tabs on the search UI in general (e.g. turn the podcast tab off).
In sum, by allowing the search tabs to be customizable, and having lenses be possible search tabs would enable users to make use of lenses more quickly. I believe this would enhance Lenses as a feature, internet exploration and improve user experience.