I was actually surprised that didn't come back in Reach. Maybe it's Megalo-able. Also, I liked sticky arming.
I'd certainly hope there is a way to add it back in, however hackneyed it needs to be. I've got no idea what hooks they have in for visual elements, but it wouldn't be just like any of the other transparent borders in the game, like Stockpile/Hill, right?
Havok if it's an overall ignorance than that's even more sad that whomever is managing the multiplayer didn't think about what people need to know when playing their game. The whole "flag stolen" when it's a neutral flag and your team mates take it still fucks with me because I'm not going to pay attention to the little words on the left hand side of the screen that says it's my team mates before I hear that announcement.
I'd certainly like to believe there was a technical reason behind all of those omissions, like there apparently is with the Score Bar and Megalo. But somehow it just feels like the basics were all that was ever made, and even then, like with that Neutral Flag issue, even the basics are just missing. Seeing the UI in that Halo 4 material, like the score bar and Back button that hopefully brings up gametype information, makes me hopeful that we'll see a return to UI design that is both functional and sleek, as you mentioned.
It's really odd how so many things - little things that add up - took steps back as the series went on. The UI largely got better, but a host of omissions in Reach (many of which were later updated) and some really strange game type decisions, such as the arming zone, take a lot away from the game.
I'd honestly forgotten how arming worked in Halo 2, but this discussion bought it all back. It was so much better when we could move around and see the arming zone.
I can see how these things get lost as the gametype emphasis changed over the series. Halo 2 was the introduction of Assault and asymmetric gametypes, and most of the UI elements we miss were developed to make those things awesome. With Halo 3, VIP was developed and had custom UI, but by and large new gametypes took a backseat, with an emphasis on variants of existing gametypes, like instant-arm Assault. Then, with Reach, obvious effort was put into their new gametypes Stockpile and Headhunter, both of which have custom UI elements (the king marker for a skullamanjaro, stockpile 'next score' timer, etc). It's super unfortunate that like so many other things, the awesome UI bits developed in the past weren't brought forward like they should have been.
Also, sticky arming was rad. It's discussions like this that make me glad that 343 dudes read this thread, so hopefully this little stuff doesn't get lost again.