You have hit the proverbial nail on the head IMO.
All of the speculation are possible answers. It is plausible, especially looking at how they have been willing to add previously unknown information/equipment to the Macross universe, for it to be a second or subsequent Macross (SDF-1) class vessel. And that is part of what is fueling this discussion. I find it interesting that some fans are unwilling to admit the possibility/plausibility, because for them it is emotionally impossible/implausible for there to be a 2nd ship that is built along the lines of the SF-1. I find it entirely logical that post SW-1 they would have built additional ships to the specs of the SDF-1 considering how effective the original was. Having said that though, I would prefer for it to be the original, even if they did build copies, because I want them to come up with a plausible well written story for explaining how and why it is there. These questions to me, along with what it was we caught a glimpse of that appears to have disabled Alto's fighter, are the big questions I want them to explain plausibly. If it is the SDF-1 and they explain it satisfactorily, I will be happy. If it isn't the SDF-1 and they explain it satisfactorily I will still be happy, just less happy.
For me, the most complelling argument for it being THE Macross is this is a 25th anniversary show, and it would be a nice nod to the original.
-Adam