Re the 29 A220's v 12 717's so the huge number of extra airframes compared to current. This is a good thing imo.
It means things like increase in frequencies on a number of routes and with the extra capacity potentially some pressure on pricing (stop laughing at me
). Also opening up MORE opportunities.
I'm thinking QF could really do more in a place like OOL where VA coughs all over them in mainline service. At times QF has/had scheduled 717's on routes like MEL-OOL vs 1x or 2x 737, and they had at on point this year I think 3x/4x 717 during the day. I can definitely see this being a thing. Add in ADL-OOL (I know the E190 was doing it and it got dropped, but perhaps it could return?), CBR can see a lot more service with frequency - to OOL/BNE/ADL/SYD (and more reliable on SYD), even some options like CBR-CNS or TSV. NTL is probably another place that coudl see some service improvements.
Other places would probably be Tassie - LST/HBA again SYD/MEL but also BNE, CBR, ADL could potentially work.
I'd also imagine regional WA and QLD will see improvements - places like MKY/ROK/GLT and BME/KGI come to mind.
A plus for regions too will be getting rid of the all-Y 717's to a more consistent (lol) product offering - not to mention the situations where aircraft swaps due to tech issues see a J cabin potentially coming and going on some routes.
It really will be interesting to see over the next 5+ years as to where the mix of 220 and 190's go - both replacing current 717 routes but also expenaidng service.