This isn't going to change a thing. The key word is "should" (only be allowed in exceptional circumstances). Not "must", but should. And it won't be difficult for an airline to claim "exceptional circumstances" either. We live in exceptional times! Notice how the maximum time is given as 7 months? That allows wet-lease aircraft to fly an entire summer season, as they always have done. It is rare for anything to last longer than that anyway so most airlines would not need to use the extension clause which would apply to concurrent periods of 7 months, not annually recurring ones as is what currently happens.
There are a number of airlines here in the UK with long-term reciprocal agreements with Canadian carriers (Sunwing, Skyservice), including mine. If we didn't have them we would be looking at massive fleet and crew reductions. That's pretty exceptional...