Contextual rendering is getting to be more common thanks to adoption of OpenType features. For example, both MS Publisher 2010 and MS Word 2010 support various contextually dependent OpenType features at the user's discretion. The choice of glyph for U+002E could be chosen according to an OpenType style.
It's worth remembering that plain text is a format that was introduced due to the limitations of early computers. Books have always been rendered with at least some degree of rich text. And due to the complexity of Unicode, even Unicode plain text often needs to be rendered with more than one font. Murray
