Think about how cool this would be, you would be able to select the text then add keyframes to it. 
I think you will need to explain your idea with a little more details.
We can already select text and add keyframes.
I understand it to a certain degree (unrelated to selection). The engine kind of supports this, but makes it difficult to represent in XML without breaking. Meanwhile, there are subtitle formats it does not support yet that also represent timed/keyframed text. So, the concept really needs a strategy,