Yes, those could be very useful features 
for the next more advanced version of Karaoke mode, for example. I also often use the technique of listening to a sentence many times in a row to distinguish the necessary words. I also miss a feature in Karaoke mode where you could check the meaning of a sentence while listening to it, like in Sentence mode.
If you listen to the text in Karaoke mode instead of Sentence mode, you can listen to the sentence over and over again by tapping on it in the mobile app, but it’s probably a matter of taste whether repeating is easier than pressing the play button in Sentence mode…