I also would like to have a universal messaging client but sadly it doesn't seem possible , just look at the recent reverse engineerediMessage apps, why would you waste all that effort reverse-engineering proprietary chat apps, when they can get (and will get) shut down by the service. Especially while better, open protocols exist.
The employee who got hacked was both using an insecure password (the exploit needs access to an admin account) and his Plex install was 2.5 years out of date.