Collision attacks on digital signatures
Manual detection of such blobs of random bytes is rather easy to circumvent, as soon as the file is either too long or non-human-readable. So for something like this to work, you would need to automate the process.

The problem is, that it's really hard to find a valid ruleset on what is a blob of random bytes and what is valid data.

An automatic detection algorithm would have to understand all file formats that should be checked. So lets say, that program could detect a Python triple-quoted comment. Now you let it check a Java file. Java does not do triple-quoted comments, but instead uses /* do denote multiline comments. So your checker does not understand that. Or you could let it check a JPEG-file, which just looks like random bytes, if your checker does not understand JPEG.

Also, triple-quoted strings with random bytes often serve a real purpose, e.g. if you have a look at get-pip.py, it has a blob of Base64-encoded binary at the end, which contains a full installation of pip. Or any RSA-keys, they also look like random bytes and it would be really easy to put something into these fields, that causes an MD5 collision.