If I may, I would like to suggest that limiting support timeframe for the LTS versions of "flavours" is a critical factor in "chasing away" users to other Distros.
Forcing Users to upgrade to more recent versions is too much a behaviour akin to Microsoft, not one that promotes "brand loyalty" or "operational" stability, nor facilitates "continuity of operations".
Just so there is no misunderstanding, I view my personal habits in using my Personal Desktop as "operations"! 
I would like to further suggest that giving more official attention, support and development resources, to each of the "flavours", would allow Canonical to convert users of those DMs from other Distros to become part of the Canonical user-base, with the consequent advantages (economies of scale and financial) that such user-base growth would entail.