Some OpenSource/DIY software projects, containing legacy C code have been rewritten into C++. There is no any reasons to stay on C if C++ available on target platform. It has everything that C has and many "free" features, which cost 0 extra bytes and 0 extra instructions.
But I think Terminal-BASIC must go through a reverse transformation. I'm rewriting core components in pure C.
The 8-bit AVR microcontrollers were primary target at the project starting point. G++ supports this architecture, as well as 32-bit ARM versions of Arduino DUE, etc.
But many interesting architextures do not support C++. I think about running Terminal-BASIC on Z80 with SDCC, PIC uCs and... SEGA Genesis consoles (MC68000 has G++ port, but the popular SDK SGEN does not support C++).