I don’t have anything to report about search providers specifically. The prerequisite features to allow a snap to install activatable D-Bus session bus services was merged though.
That work took longer than I had expected, as we didn’t have a good way to control long running services in the user’s session. So part of that work involved creating a way for snapd to stop those services when snaps are removes, or restart them when snaps are upgraded. It is mostly complete now, with only a few more tasks to have it enabled by default.
With that in place, all that is required is some code to install the configuration file linking the activatable D-Bus service and desktop file for the search provider. I haven’t done any work on this last part, but I don’t see it being particularly contentious compared to what has come before.