ISOM 2017 was published last year, the latest revision can be viewed / downloaded from here. Enjoy reading it during your quiet Christmas holiday!
Berkshire Orienteers have produced a handy little guide to the main changes here, many thanks to them.
The key changes are to the maps themselves, which will all have to be reviewed/revised to comply. This will involve physically re-assessing runnability.
Planners in particular need to note that the map overprint (course) symbol sizes have changed, and need to be enlarged according to the map scale. Currently the settings in Purple Pen have to be manually modified to do this, on a 1:10,000 map (many of ours) the control circle size needs to be 7.5mm (ppen, will scale the Start/finish symbols to match this), the line width increased to 0.52mm, and the control number height to 6mm (regular not bold). Ask for some help if you are planning.