Hi aurel90,
A rhetorical question? Or an old chestnut?
It's 15 years since I flew an A320, and the only QRH I have to hand is even older than that. I'll try to stick to your precise scenario, which may not be typical. (You will, of course, have tried to restart both engines first.)
Sully might disagree that "obviously the only option to avoid a forced landing is to go back on the opposite runway where you just took off," and indeed it might not be practicable, for a variety of possible reasons.
My old QRH drill does not include any attempt to start the APU, although it does acknowledge the possibility that it might already be running for some reason (returning to base under MEL provisions with one ED (engine-driven) generator u/s, for example). However, my first comment on PPRuNe after hearing of the Hudson ditching was to opine that I hoped they'd started the APU, and that soon turned out to be the case. If it's available and there are no contra-indications to starting it, it's a no-brainer.
The reduction in battery endurance on the first failed APU-start attempt would nevertheless leave remaining battery endurance far greater than the endurance of the a/c, even if it happens in the cruise. IMHO, however, if the scenario begins at high altitude it might be worth considering delaying the first attempt until medium altitude in the glide, by which time the APU may have warmed up a bit. Failure of both engines is a completely different situation from a failure of all ED generators with one or both engines running, in which you might need (and be able) to fly on RAT and BAT for an hour or more.
There is a possibility, IIRC, that limited Green and Yellow hydraulic function may be available from windmilling engines in some cases.
With the APU running:
(1) all electrics are restored, including all ELACs, SECs and FACs;
(2) Yellow hydraulics can be restored with the Yellow AC pump, although Flaps will be slower than usual as the AC pump is less powerful than the #2 ED pump;
(3) Green hydraulics would be available via the PTU, but I can't comment on the advisability of using Green services. Someone else will comment. I imagine that it would still be advisable to use gravity extension for the L/G, which would also avoid any temptation to use the NW steering after landing? As for normal (Green) braking, similar considerations may apply, although the automatic transfer to Yellow brakes is, IIRC, swift.
Why would the 7 applications/releases of brakes you say are available from the Yellow brake accumulator not suffice for landing, even on a short runway?
Your choice of an 1800-metre runway for the return suggests that a slats-only landing would be challenging, so restoring Yellow hydraulics would be helpful, to say the least.