Today, the read more link generally inherits the style settings of the entire excerpt. Since it's a link, you can adjust the color by using the experimental link color feature, and since it's inline text, you can use options like Bold, Italic, etc.

The alignment cannot be adjusted independently, and neither can the font size.

I expected the read more text to be a standard, separate child block that would have its own set of controls. Adopting this implementation would allow for a wider range of design options. (Maybe even the ability to change the link into a button?)

GIF of current state: