I also support that request! We're using the BitBucket as well and have the very same workflow as described.

In our company we're aiming to use the subrepo approach as well.

AFAIK there's currently no GIT GUI that natively supports the suprepo "feature".

Meaning: In case SmartGit would support the subrepositories in a GUI this would be a unique selling point!

Therefore: A clear vote from my side!