I believe you can easily reach 9600 baud with Ice-T, maybe even more, and that means it can possibly be used for serious terminal work (I use vi(1) for everything too).
I don't plan to use SIO2PC to emulate a disk drive (I prefer SIO2SD and real disk drives for that).
If anyone is familiar with Ice-T let us know how you can send ASCII 123 and ASCII 125 codes from it.
It is possibly also doable using keymaps(5) on the Linux side, but I am still waiting for the SIO2PC adapter to test all this.