Once FromSoft manage to unfuck the camera situation in their games I hope "boss room is a flat circle" meme dies off and they make more interesting boss arena with obstacles and other bits of terrain that you can make use of to your advantage, with appropriate boss gimmick too. Something like fighting mega cancer dragon that have much higher rot breath frequency but you have a few tactically placed boulders/rocks littered around the arena that you can use as cover, or ultra frenzy flame boss that does a no damage madness buildup attack from far away that you have to hide behind seamless covers and run to him when he's not doing it.
If Elden Ring gets another DLC, I hope Miyazaki put in some platforming in the boss arena for lulz. At least dying because you suck at platforming is funnier than dying to bosses with bazillion anime attacks.
If you'll notice one thing about how From designs anything, it's always in reaction to what did and didn't work according to the public. Notably, what you're looking for is almost every boss from Demons' Souls. Most of them are puzzles, and people didn't take well to it. Dragon God notably has a lot of hiding in and out of cover mechanics and people at the time hated it. They'd carry a couple of "puzzle" elements in boss design with fights like Gwyndolin requiring running in and out of cover and the infamous Bed of Chaos fight. The issues was those weren't received that well either. You know what was well received? Manus, Artorias, O&S, etc. While O&S have a psuedo-puzzle in keeping them seperated and deciding which one to beat first so you have an easier or harder time in phase 2, the DLC bosses in DS1 are, in my opinion, the real start to the design of the following games being run to the hard boss rather than focus on the level. It really didn't help that the following game, Dark Souls 2, was very poorly received and had almost all of its design choices tossed out like the baby with the bath water. It wouldn't be until Elden Ring that they'd return.
What's really funny is that you can see some responses to base game complaints being kinda addressed in some fights in the DLC. Divine Beast and Romina have those delayed attacks with fast hit-boxes, but they have big tells for when they're about to actually attack out of their long wind-ups like Divine Beast snapping its mouth close on the delayed head slam and Romina's stinger slam having a huge glint and "glint noise" (I don't know how else to describe it). That being said, the game never capitalized and iterated on lessons learned from Sekiro. To be fair, even Miyazaki admitted to this fact and he expressed surprise the game was even as well received as it was.
There's a possibility they actually iterate on Sekiro's design, and that game did have quite a few puzzle / gimmick fights, but a lot of the best received fights were just duking it out with a dude in a flat arena.
TL;DR: I think fighting guy in flat arena is probably going to stay the main way bosses are fought, and it's mainly due to the fact that most people don't complain about uninteresting arenas specifically.
Edit: In fact, the most interesting arena they ever tried was probably Bed of Chaos and it still remains as one of their worst executed ideas to date.
