Maybe I’m a fast reader but the first example didn’t bother me and the barely changing text also enhanced the comedy of the scene showing their back and forth.

Differently coloured borders are another point of contention for me. In many fansubs I found that they drew excessive yet unnecessary attention. I feel a style change (italics) indicates an interjection more subtly, and lets the voices/audio do the talking (“Look, italics instead of roman; this must have something to do with the third voice interrupting them”), rather than drawing viewers’ attention overtly to the fact that there is something different there (“Look, different colours! Something has changed here.”), In messier situations (e.g. with three or more characters talking on three or more topics), or when there is a lack of visual/auditory cues, I would definitely consider changing border colours. This is a matter of preference though; I just prefer my subs on the subtle side.

I’ve also seen horizontal repositioning, particularly in L-E’s Nijuu Mensou no Musume, if I recall correctly. I found it quite disorienting; fansub viewers are subconsciously attuned to expect subtitles in the middle, so unless the situation calls for it (e.g. character coming in from off-screen in the midst of a complicated conversation), I try to meet those expectations.

I’ve actually considered even crazier stuff, like “manga-style proximity subbing”, if you were wondering ;D (might still have a few videos of those around, I’ll see if I can put them into a future post.)