Can Canonical and the Ubuntu community create a bounty fund, as a single pool of money, to encourage more developers to contribute to Unity. I'd suggest Canonical starting it off by funding a bounty pool, where fixing 1 bug counts as 1 share of the sum of money. The Ubuntu community could then contribute additional funds if they wish.
I'd suggest the following procedure:
Developers need to complete one bite-sized bug to be eligible.
Completing (i.e. the bug is marked as “fix committed”) a non bite-sized bug gets the developer one share of the bounty pool.
More complex bugs could carry additional weighting and count as 2 or more shares.
Developers who've already completed bugs get one share per bug completed to start with, therefore rewarding them for their contribution.
I think this would encourage more developers to join in Unity development and give existing developers further incentive to fix more bugs. It also provides a way for non-developers to feel they are helping with the software development. No specifications would need to be written up.
If this or something similar could be made to work for Unity, it should also work for other open source software, e.g. Libreoffice, Mozilla Thunderbird & Lightning, etc. Which would give a much needed boost to open source on the desktop.