I'm just going to hijack your conversation here
Section 2.3 of Canonical's agreement says this:
Based on the grant of rights in Sections 2.1 and 2.2, if We
include Your Contribution in a Material, We may license the
Contribution under any license, including copyleft,
permissive, commercial, or proprietary licenses. As a
condition on the exercise of this right, We agree to also
license the Contribution under the terms of the license or
licenses which We are using for the Material on the
Submission Date.
They have the right to make the software proprietary, but it must be in addition the license of the software when the contribution was accepted. Unless I'm misunderstanding this, since Mir is licensed under the LGPL and GPL, they could never dual license it with a proprietary license.
If what I said is true, I'm not worried about the CLA.