You can set a placeholder image, sure.
As to the other questions, I dunno. There isn't a real 'need' to format text IMO - I mean on a gridscreen your description just shows up in the description box, the limited space available for most of the text features of Roku makes it rather pointless to concern yourself with different justification, tab spacing, or formatting. Having text in bold/italics/different font sizing on a word by word or individual letter basis would be most confusing to anyone trying to read it anyway.