The Cseries could do everything the A319's do today, more efficiently, so hopefully more based aircraft and more routes could end up happening (maybe, one day, in my dreams, I hope)
Your example today, in a perfect world, we might see Bristol and Belfast go back to their old, real, useful schedules 2/3 daily, a London route could become feasible again, say 2/3 to Stansted. Berlin, Geneva, Nice, Jersey, Split would be good contenders.
In terms of new routes, Milan, Venice, Budapest, Amsterdam, Paris, Hamburg, Reykjavik, Marrakech could all be feasible additions with next gen, fuel efficient aircraft... All we need now is for someone to buy them, and easyjet has expressed a lot of interest.
3 CS100
1/2 A320neo
1 A321neo (perhaps seasonal)
Would be fantastic 10 years down the line IMO, and I don't think it's necessarily that unattainable