Yes the "special needs" notion is a slippery slope.. how wide open is that? A bit like th enotion of being eligible for early voting in elections where, in theory, you need to have an appropriate need yet this is not enforced by the AEC (I was asked if I was eligible the other day, but not to express why). <---- keeping it topical
I suppose on domestic flights, there's nothing "special" in the fwd lav as in extra nice amenity or anything.. it's just a tiny place to do one's business.. in Business.
This only really seems to be a 737 thing and on short -medium haul routes. I've never seen pax come fwd on the 330 for example, but they also have far more lavs spead out (and indeed, more than J!) and same on 787 let alone 744 or 380.
I have seen queues and once or twice have seen pax redirected, but it seemed to me more to free up the space around the galley and say to them "Well you can use the lav down the back" rather than "If you're a Y passenger you need to go back there"
There's also the notion of security - I know it's more relaxed in Oz, but the "Stay in your ticketed cabin" thing is far more tightly policed and made note of on US carriers than it is on QF... the less people goiing forward to that lav by the coughpit is probably the better (but this is no way is to imply anything about the nature of either J or Y passengers in terms of seucrity risk - as we know they can be anywhere).
In general I do not get too fussed by Y pax using the lav if they're in the fwd Y cabin unless there's a demand for the facilities from J at any one time, which is pretty unusual.
Me, I do my best to avoid the lav full stop