I think that in general the compatibility argument outweighs any potential small benefits that changing item placements might have. I looked at the changes being suggested and I don't really like them very much anyway. There might be a few that would be small improvements, but most of them seem to be rather pointless, and there are some that I think would definitely be bad.

"For online, item placement doesn't seem to make a big difference from what I've read. So it's just speedruns that would be affected ..."

If it wouldn't make a difference for most players in any case but it would negatively affect a few players, that seems like a reason to not make any changes.

It's still possible to finish without the checkline glitch by going on the off-road and finishing in front of the lapline even if it's slower. In any case, to be consistent runs with the checkline glitch should be retimed for all tracks even though it's much easier to get on some tracks than others where it's available.

Also, I noticed that on Beehive it's possible for the timer to be off by up to 5 ticks by finishing near the rightmost part of the lapline. This is the same amount of time that's saved by the checkline glitch but there doesn't seem to be a checkline here. Some of the current runs are about 3 ticks faster than the true time which is a noticeable difference already. I'm not sure if anything should be done about this though.

In 1.1 rc-1 it seems that the "Challenge Completed" skip can be used normally from the first challenge without having to reset anything.

Animtrack should not be added, in view of the following considerations (in addition to what Fouks has said above):

1. The graphics are awful.
2. The track has numerous bugs. The rescue is broken, there seems to be a slowdown in one part, restarting after the lava has filled up doesn't work correctly, and the floating timer doesn't reset properly.
3. There is only one checkline, which means that a checkline exploit is possible (Andet has already pointed this out somewhere).
4. From a speedrunning perspective it's very problematic that almost the entire run is dependent on cycles. In certain sections it doesn't help at all to be fast, because it's necessary to wait for the moving obstacles to get out of the way anyway. The only part of the run that really makes a difference is the last 20 seconds. In every main game track and all of the add-ons here, it's good to be as fast as possible, while in this one it's more about being fast enough to not be a cycle slower.
5. It's really not very interesting, and certainly not even close to being "the hardest track in STK ever" as claimed in the description. The track is linear, so there are no difficult turns anywhere. The road is wide enough such that getting skids, if even necessary, is easy. The main difficulty is supposed to be avoiding the obstacles, though they follow a predictable pattern so that's fairly easy as well. It's not particularly skillful to run compared to almost any other track listed here.

I don't like Nostalgia very much either. It looks ugly, the accelerators in the tunnel don't work very well, it has some unintended shortcuts (and one of those has just been patched, meaning that Andet's run is no longer valid for the current version of the track, which is another problem), and three laps in time trials is too long. Since Subsea was removed just for having a similar problem with an accelerator I think that it would be fair if Nostalgia were also removed.

I haven't tried to compile it yet, I just did it without the mod because Andet had already ran it and didn't use the mod either.

The difference between the elapsed time and the interpolation should always be less than one tick (although it sometimes isn't, especially if the finish occurs at the edge of a lapline), so it only really makes a difference when more than one run has the same elapsed time. In such a case, I feel like it would be fair to consider the runs tied and it seems a little arbitrary to decide that one run is a few milliseconds faster than the other. But it's very rare that this is the case, so maybe at least for now it isn't much of a problem.

The bigger issue is the glitch that finishing on a checkline sometimes (it doesn't seem to be entirely consistent, it may depend on precisely how the finish is approached) results in the time shown being five ticks faster than the elapsed time. This can only occur in tracks where a checkline is placed on a lapline (in 1.0, the tracks affected by this are Antediluvian Abyss, Around the Lighthouse, Oliver's Math Class, Volcan Island, and Zen Garden). Perhaps it would be possible to just remove such checklines in future versions.

As for compatibility between 1.0 and 1.1, for some reason I was under the impression that the upscaled version of Zen Garden was going to be used in 1.1 (it was intended for 1.0 but was accidentally reverted), in which case runs of that track in 1.1 would of course not be compatible with 1.0. I don't think it matters very much if it's going to be used, though, so if it's considered important to maintain compatibility, I think it shouldn't be changed.

The replay file time rounds up to 1:24.549 anyway, so that's fine. A checkline in XR591 was modified in the Git version to make it possible to cut off more of the last corner, so runs in the Git version could be slightly faster. But there are no other gameplay changes between 1.0 and Git that I am aware of, so I think that it would be possible to accept Wax's Snow Peak and Volcan Island runs.

It is certain if Wax's Snow Peak time is 1:24.548 or 1:24.549? Because if the fourth digit of the ghost replay filename is 5, then the time shown at the end screen is rounded up or down depending on the exact time in the ghost replay file, but after closing the game and reopening it the time is always shown rounded up in the high scores list. For instance, my Fort Magma run shows 1:24.863 in the end screen and indeed the time listed in the replay file is 84.863457 (so it should round down), but when I look at my high scores list now it shows 1:24.864 as the time.

Some egg hunt tracks could be added: Beehive, Blackhill Mansion, Canyon 42, and Lake Ikeal. Green Hill also has an egg hunt, but there's only one egg and it's very easy to get, so I'm not sure if it should be included.

I have enabled e-mail authentication.

Andet's times for Paradise Peaks and Tux Tollway should be 2:10.692 and 2:17.486.