It's now used for more than just stream protocol (e.g. pin protocol), so don't use false names.
These symbols are still defined in terms of the system Exxx symbols, and can be switched to internal numeric definitions at a later stage. Note that extmod/modlwip still uses many system Exxx symbols.
Currently UART(0) and UART(1) are exposed and only uart.write works.
Paul Sokolovsky