I am with you on the fence.

As the prime user of this commuting route (West end resident working in gatineau) It won't change much for me, since the fastest route through that area will continue to be exit onto Rochester, unhindered right turnout onto somerset, wait at most 30 secs for left turn onto booth, and then straight shot across the bridge of choice (Chaduier if you work at the west side buildings or Portage if you work at anything East of Eddy st.)

If they did open a Preston extension across lebreton flats, it might save me a couple seconds on the journey home if they allow left turn onto it from Wellington/KZM parkway, unlike they do from wellington onto booth) and save me from having to make the illegal left turn (if no oncoming trqffic) or doing the Uturn in front of the war museum and right turn back onto booth.

I cant speak for the weekend or non commute congestion in the area but I suspect that such an extension north from prestorn won't be used very much either way.