I'm not the OP, but as a child growing up in an anglophone country but with a 'low-prestige' accent (think Indian English or Singaporean English), it was ingrained to me pretty early on that the only 'proper' ways to speak were RP or General American, and one of the reasons was because all the kid shows I watched had characters who talked almost exclusively in those accents. 'Exotic' accents were used mostly for comedic value.
Having a greater variety of shows that model the diversity of the English language would probably have gone some way to dispelling that damaging self-belief? I really love the existence of shows like Derry Girls, because they make me less self-conscious of my 'exotic' accent.
But why would TfL replace their old school displays with LED displays if the latter cost more than the former in the first place?
If they are gaining some sort of monetary incentive from replacing poster displays with LED screens, and your reasoning holds true, then perhaps in the greater scheme of things the LED displays do use less 'power'.
Having a greater variety of shows that model the diversity of the English language would probably have gone some way to dispelling that damaging self-belief? I really love the existence of shows like Derry Girls, because they make me less self-conscious of my 'exotic' accent.