I really like this pedal, i think it could have some very interesting mods. I also recently saw a pedal called the Z.Cat Delay/hold, which had the option of delay with tap tempo and chorus aswell. I'm not sure how easy it would be, but i think it would be very interesting.
I'm fairly certain the Freeze pedal is a digital thing. I'd love to see something like that in a DIY project, but I think it unlikely to be possible. I'm not an expert, that's just my couple years of experience in building so far.
There are delay pedals with tap tempo as DIY projects available. Check out just about anything with a PT2399 in it, and then look at this: http://thoughtprocessinc.com/ (http://thoughtprocessinc.com/)
That reminds me that I have a PT80 with a PTAP that I need to debug...
Jacob
I'm sure that it is DSP.