. . . . Is Magix planning to support srt files for subtitling or do I have to bye another editor and stop using Magix . . . .
That depends on what the final destination of your video is and exactly what you want to do -
subtitle videos for exporting and uploading to the likes of Youtube
Youtube have their own subtitling systems - see here, for others sites check their support pages.
subtitle videos for exporting and playing directly in a media player
There are several third party programs available which will add the subtitling into a video file however you are limited to certain file formats and not all players will be able to use them.
subtitling DVD or Blu-Ray discs.
Magix DVD Architect supports subtitling, I use this in preference to the Movie Edit Pro and VPX disc burning options because it gives you much more functionality over the features you can incorporate in the discs, eg full customisation of menus, sound/captions on/off, multiple language/audio tracks, play lists and more.