Thanks for the more detailed proposal. It's good to see some concrete ideas about this search project.
In response to some of the items that you listed on your draft proposal:
Text based AIR
Query can be any text say 'rock' or 'beethoven' etc and the system will search through the text(tags, artist name, description) associated with the audios and will return list of relevant audios corresponding to matched text. It's simple to implement but doesn't help much in audio retrieval as most of the times the audio doesn't contains enough annotations.
In AcousticBrainz we do have a lot of annotation data, including all of the information in MusicBrainz, which we can access via the MusicBrainz IDs which are used in both projects, and also the generated annotation data, which you listen in your post. For me me this would be an ideal first part of the project, combined with some sort of visualisation of the data.
Vector Space Model(VSM)
This is a basic yet effective model. The idea is to represent every audio entity in vector form in the feature space.
This is a good idea, and is something that we can already do in Gaia. Was your idea to implement this from scratch, or use an existing system? If you were to do this, we should also do a comparison between the system you want to use and Gaia to see what one works best for our requirements.
Spectrum analysis(Fingerprint) model
This relies on fingerprinting music based on spectrogram.
The data in acousticbrainz isn't detailed enough to build a fingerprint model. Additionally, MusicBrainz also has a fingerprinting system which it uses (https://acoustid.org/). Building and maintaining an additional fingerprinting system is probably too much work for a Summer of Code project, so I don't think we would want to go with this idea.
Deep Neural Network Model (Deep learning Approach)
This is something that we've just started to experiment with at the Music Technology Group. We see this fitting more under our "Dataset building and model creation" section of AcousticBrainz, instead of search, but it is definitely something that we're interested in. If you want to investigate more in this direction, you should add some more detailed information about how you think we could go about this project.