The 80% rule can be looked at in a few different ways. On a positive note, once we get to a point where NO country wants to export anything, at least we're ONLY giving away 80% to the US. Assuming that our population stays at 10% of the US levels, that still gives us double the amount per capita that the Americans will be getting from us (assuming that the US didn't have any to start with). So it's probably a fair number in that respect.
In the shorter term, for the next decade (hopefully) while we can still afford to export energy, the big drawback with the 80% rule is that it significantly constrains our ability to divert production to higher-paying customers overseas. So the occasional comments seen here and on Stockhouse about "let's just build a big pipeline to the coast, and start selling a lot more to China," have to be tempered by the Free Trade Agreement restrictions.
At least, that's the way that I understand it all. There are probably other factors that I'm not thinking about, because I've never really expended a lot of energy thinking about the FTA.