That is very cool, at least as an end in itself. I certainly don't want to discourage or minimize the effort expended, but it strikes me as more of a solution in search of a problem. From my perspective, these are must-haves: (1) Tabs in the IDE. Any project of more than trivial complexity quickly morphs to multiple files. (2) Ability to define board types. I do this both to experiment and to implement completed projects. (3) Ability to use Arduino-Tiny or other alternate cores for other MCUs. (4) Ability to program MCUs either via a bootloader or an ICSP programmer.
Maybe you have a problem statement to share that might make the light go on for me?