I couldn't find an existing ticket, so let me try my luck.
I would like the ability to search for GeoJSON points that are within x meters of a GeoJSON Polyline. This is currently a costly query to implement outside of a database server, as I either have to; build a Polygon from a Polyline before using a $geoWithin, or hit Mongo multiple times using a $near, then filter all results for a distinct list of Points.
An approach that could be achieved in the server would be (likely a naive implementation):
1. make a LineString into a 'complex' LineString by reducing the distance between each point to a small distance. JS example: https://github.com/rwt-to/GeoJSON-Tools#complexify
2. convert the LineString into a Polygon by creating a circle out of each point in the LineString, then merging them (haven't found an effective way of doing that yet, my Polygons become huge)
3. use $geoWithin internally to find Points in the Polygon.
The second approach would be to perform step 1. above, then just use a $near for each point in the LineString, then filtering all the Points before returning a result.
In case I haven't explained it clearly, here's a SO question explaining the issue: http://stackoverflow.com/questions/19015861/find-points-near-linestring-in-mongodb-sorted-by-distance
There is likely a more efficient way, but I haven't had the time to try find it. I think the query would still perform decently if ran internally on Mongo, as either method above would use indices while avoiding round-trips.
Lastly, just for control, it seems like this is easily achievable in PostgreSQL : http://stackoverflow.com/questions/10286899/find-the-nearest-points-along-the-linestring-in-specified-distance-limit-and-ord