I'm actively working on MAME again after a short decade or so break I've catching up on all the C++ enhancements that have been made since I worked on it last.
I'm trying to finish off the Mattel Intellivision Keyboard Component Driver (intvkbd). I've been updating the CRT5027 CRT Controller device to overlay high-resolution text properly over the Intellivision display. I have put one of my reverse-engineering tools online, a cartridge image which loads a 6502 monitor program into the actual hardware via the Intellivision cartridge slot: http://github.com/palazzol/kcmon
I have a lot of recovered data from the tape drive. For step one - I'll be taking some recovered data, the "Family Budgeting" BASIC program, and getting it to load into the emulator. I actually have this working in an ancient version of MESS (2003?), so it's just a matter of porting it over - however, the tape format I used is not sufficiently general to support the other tapes. I'll post some screen shots when I get this working.
I need to define a better tape format, probably building from the existing cassette support in MESS. The tape drive is a fancy 4-track device, with 2 audio and 2 data channels, one of each are read only, the other 2 being read/write. Hopefully I'll be able to verify the validity of the other existing tape dumps. The BASIC programs use only a subset of the tape drive, and none of the Intellivision graphics and sound. But the more sophisticated tapes use the full capabilities of the Intellivision plus interaction via the tape drive.
As a last step, there is a microphone input which can be used to record audio onto the audio track. As I understand it, MAME has no existing support for audio input, so I guess I'll save support for that until the end.