Canada

However, PR, and especially MMP, would naturally create an imbalance, necessitating either seat adjustments or additions (which increases costs), which could likely trigger 7:50. Any meaningful Senate or Governor General reforms would definitely require it.

It is not necessary to change the number of seats as you can still have MMP system with the same 338 composition dividing them into 207 regional seats (67%) and 131 regional seats (33%). The Sections 40 and 41 of the Constitution Act 1867 clearly empower the federal parliament to alter its own election rules, it simply requires a majority of the house to vote in favour. The issue is that too many establishment politicians in the CPC and the LBC refuse to commit to the necessary action that leads to electoral reform, thus we the people must pressure them greatly to do whats right for our country.