I actually had checked out your ATtiny10 IDE earlier after you posted about it on the Developers mailing list and that was what prompted my question about GitHub. Yesterday when I looked at the debugger project I thought I hoped to see a link to GitHub but figured you probably just didn't have an account.
Since you're looking for feedback I'll go ahead and give my $0.02 but I actually know practically nothing about on-chip debugging so it's not worth that. Over the last week I've been listening to a lot of episodes of Embedded Podcast and they seem to have been on a campaign to get people using debuggers lately. I've always thought that the combination of AVR microcontrollers, the Arduino IDE, and a poor hobbyist's budget were not a good match for on-chip debugging but this made me want to have a closer look at what it would take for me to do this. I discovered they are selling JTAGICE clones on eBay for $5 USD! This made me want to just hit the "Buy" button and give it a try. Looking closer it seems this debugger only supports a limited set of AVRs which does not include my primary target (ATmega1284P), and I'm back to considering a >$50 investment. So I'm very undecided whether I want to spend $5 just to get my feet wet (I do have one of MCUdude's nice dev boards with ATmega32 and a JTAG breakout) or whether I should put that money towards the "real debugger" fund instead.
To me, your project is very cool because it takes something that seemed quite proprietary and commercialized and opens it up to anyone with even a small amount of experience with microcontrollers and hardware they already own. As far as being practically useful to me, well my current goal is to use GDB with ATmega1284P so probably not so much but that's just me. Obviously your project is for chips that have debugWire and that's likely to be a hard limit. As for GDB support, I have no clue whether that would ever be a possibility.