Could you please check whether you can successfully compile and upload https://github.com/maxgerhardt/pio-timsp430-new-toolchain-example? A base example should be prepared there, attempting to place some functions into HIROM and printing their addresses via UART.
The platform code was altered so that no custom platformio.ini modifications are necessary anyore – the board has by default the full 128kByte and the compiler is set up for the large memory-model, with -mlarge -mcode-region=either -mdata-region=either.
Since I do not have a board, I cannot test it however – compiling works for me.