I want a casting function for the same reasons as many of the other users posted above.
First, the reason I use MxPlayer and not a video caster app is because I get videos from all over, of varied video formats, some with multiple language audio subchannels, and the video casters don't handle this as well as MxPlayer. Most caster apps have limitations to what file types they can cast, and most caster apps won't let you choose the audio language. MxPlayer handles multiple formats and language subchannels better than anything else I've tried. I also like the easy zoom and audio volume adjustment MxPlayer provides. This is my favorite video player.
Second, I stream most of my video to my TV from my tablet with chromecast. Because MxPlayer doesn't have a native cast function, when I play videos on MxPlayer, I have to mirror the screen with Google Home. Now this wouldn't be a big deal, but I also like to multi-task. I browse the web, read books, play games while the video is streaming. I can't do that when mirroring the screen. So I'd love to see MxPlayer develop a cast function where I can play any video format, set the audio channel to English, start the cast, and move on to other things on my tablet.