At the anti-censorship meeting today you mentioned talking to ICLab about testing the default bridges. I believe that ICLab is already testing at least a portion of the default bridges; they may have data that you just have to ask for.
OONI and ICLab test the default bridges as a result of my, Lynn's, and Qi's asking them to while we were studying default bridge blocking. The data exist but we never carefully analyzed them. You can see what little analysis we did at https://arxiv.org/abs/1709.08718 Figure 1 and Section 5.9.
The data we used is in data/iclab/tor_jsons.tar.bz2 in https://repo.eecs.berkeley.edu/git-anon/users/fifield/proxy-probe-paper.git. It's a lot of JSON files that have TCP connect, TLS certificate fetch, HTTP fetch, and TCP traceroute for each destination. We sent them the list of bridges in September 2016 and they started measuring shortly after that. The most recent update to the bridge list we sent them was in August 2017 for https://bugs.torproject.org/23166.