I really think, that it's absolutely sufficient to search only for the page title, not the content itself, like it was before. People (will) use this plugin primarily as a launcher, and not as a search tool, because Zim's search is already intuitive, fast and even shows a ranking for quick orientation.

In that case you would significantly speed up the searching process. In case of need, I also can imagine separating the results for the page titles and the content. This could be configured in zim > options > plugins > zimsearch.

So the results of the page titles would appear nearly instantly in the first section in Gnome's activities overview, and after some seconds, underneath, another section with the content results would appear. By this we would have the best of both worlds: instant title results with additional in-depth content results.