A friend of mine and I did MEL-LAX (789) recently with no issues with changing to and from our PJs. We both used the ADA bathroom which was more room than I ever needed.
I just used them while sleeping and changed out of them once I'm done. No real issues for changing in and out of the PJs for both of us (and I saw plenty of people in their PJs).
Keep in mind that they only issued on flights 12h+ so there shouldn't be much of a crowding issue IMO.