That would be great!
I've been thinking about this and realising my own limits.
The only thing I know for sure is it must be simpler than most of what we and others have been talking about since 2003.
As a very simple approach, I thought of making happiness the base allegiance meter for the current owner empire and live without a meter for allegiance to foreign empires. No problem when there is only two empires competing for the allegiance of a colony (foreign allegiance rises when happiness declines). Problem is when two or more foreign empires are trying to influence-conquest the same planet, but I got this: Say empires A and B are trying to overthrow government of a colony of empire C. Happiness of C will decline due to the effects of A and B propaganda projects. Once it reaches 0 the planet does not go for A or B, but stays in revolt (happiness 0) as long as both empires keep active their propaganda projects, and once one of A or B gives up and stops its propaganda project the planet goes to the other empire and begins rising happiness. Probably there are more complex (and probably more interesting) ways of representing opposing effects, so that one could be stronger than the other and actually beat it without requiring it to give up first.