Regarding potential overcapacity during winter, one should also keep in mind that several planes will have to undergo C-check during that period, making overcapacity lower than we think.
Though that sounds right, if you think deeper it's not.
Several planes had to undergo C-checks the other years as well during the winter. So the new additional capacity comes on top of that anyway, worse even in the future they will have to send those additional aircraft to heavy maintenance as well.
Depending on what needs to be done, an A320 C-check costs from one to several million dollars every 18 months. That's the C-check alone, it doesn't count light maintenance.
Also, the "bigger aircraft" for more capacity reasoning doesn't work anymore as most RJ85's were already phased out/stored or in phase-out maintenance by early last year.
If SN can hold up that long, I hope that they revisit the Africa narrowbody concept using the NEO's.
I can't comment on more transfer pax without seeing concreet figures.
How many is that on a daily basis?
Also, one has to think whether these are significant enough to be considered, including the yields.
The Intra-Europe market is well-covered by point-to-point, so it's either people flying on cheap corporate contracts that force them to transfer through Star/LH hubs, leisure people who would go out of their way to fly cheap (but no FR/U2 option), or people flying from/to a handful of regional airports in the U.K. and Italy that SN is covering well, from which there are no direct flights.
I already said that SN could expand into the shorthaul transfer market by increasing the regional destinations, but so far there is no evidence that SN has seen that hole in the market.