It seems that sprocket's developers doesn't want to change this behaviour.
On the other hand, I agree with you.
MD5 digests enough for asset pipelines. MD5 hash calculations quite fast and it is nearly impossible to get same hash value for the same asset with additional benefit of smaller digest size.
You can use MD5 digest with the following change on
config.assets.configure do |env|
env.digest_class = Digest::MD5
After that you can compile assets:
rake assets:precompile RAILS_ENV=production