OK, I have found how to do it in another post. Send a POST to request to http://IP/DIAL/apps/[app_id].
curl -H “Content-Type: application/json” -H “X-Auth-PSK: sony” -X POST http://192.168.2.4/DIAL/apps/com.sony.dtv.com.google.android.youtube.tv.com.google.android.apps.youtube.tv.activity.ShellActivity
Also found another way:
curl -H “Content-Type: application/json” -H “X-Auth-PSK: sony” -X POST -d ‘{“id”: 1, “method”: “setActiveApp”, “version”: “1.0”, params: [{“uri”: “com.sony.dtv.com.google.android.youtube.tv.com.google.android.apps.youtube.tv.activity.ShellActivity”}]}’ http://192.168.2.4/sony/appControl
Which seems a bit nicer API.
So my PR is not really useful for that as that one sends commands to /sony/IRCC. Both sony_bravia_ha and sony_bravia_psk packages would probably have to be extended to support that.