Yes, a very good one. SFML events are handled on the user side by polling the event queue, not by callbacks. And I don't want to completely redesign the event handling in SFML.
We could argue hours and hours about technical stuff that
can be implemented, but it's really not important, I care more about design issues. So if you want to suggest new features you should start by thinking about design, and how it integrates to the SFML API. I can then handle the technical side