We should definitely add this to Highmaps, possibly as a plugin. There are available tools for converting to and from GeoJSON/TopoJSON: https://github.com/mbostock/topojson. Assuming these are licensed such that we can use them it might not be a lot of work to add support for this. Adding native export to TopoJSON for the map collection would be a lot of work, so hopefully the GeoJSON converter does a good job of detecting topology on its own.

Hope you add this soon. TopoJSON files are so much smaller.

There's also a compressed GeoJSON variant that does a similar task - https://github.com/mapbox/geobuf

topoJSON seems to be having a smaller file size in comparison to geoJSON for the same shape file.

I agree...we have been developing map dashboards using d3 & Leaflet but Highcharts is more interesting & easy to use. Would request support to load TopoJSON.