Uniden wasn't working on the x36 and HP2 at the same time. The x36s were released in January, 2014. The HP2 was released in October, 2014.
True, they were "working" on the dongle firmware, but they didn't get a working copy until December, 2014, so it's highly unlikely they were working on more than one project at a time - at least not any significant work for the dongle aside from seeing that it still didn't work. Who knows - if everything had gone according to plan, the HP-2 might not be out yet, or just be announced.
From December, 2014 to current, it's pretty obvious they have been working on the dongle firmware and Siren app.
I don't know why they haven't had any updates for the 436 either, but I'm sure once they do it will be obvious as to why not. I bet a lot of it has to do with the unfinished code for the dongle which is likely shared in the development between both x36 models since they are nearly identical. So, it may not have been Uniden's choice.
As for what should be done, well, Uniden should have gotten the dongle firmware in December 2013, not December 2014, but that obviously didn't happen.