Who am I, but okay, my personal answers and ideas...
So, with or without BOM
I see advantages in having a BOM and in not having it. Answer: do as you like.
Just make sure the BOM is not present atthe start of every line, as happened in one upload a couple of days ago. DIfficult to detect, almost or totally invisible for text or subtitle editors/viewers, but causing trouble in VLC (and probably a lot of players). You will get this:
So, "..." or "…"
Same same, I think you already said it yourself, both have advantages and disadvantages. I would say do as you like, but personally I always use three dots, mainly because I rather choose for simplicity (easy, reliable) instead of fancy stuff, especially if not necessary. Hallelujah for smoke signals, they even work when it's windy.
So, "-What" or "- What"
Same same, do as you like. Personally I think - followed by a space is more beautiful, so this is what I always use. Some say it MUST be without space (including the very professional Dutch Hoek & Sonépouse), others say it MUST include a space. So...? I think most important is to use consistency. Do as you like, but stick to one method throughout the whole subtitle (or even all your subtitles).
Btw, different languages have their own different guidelines. In Dutch, in dialogs, only the SECOND line has a -, NOT the first line, In English both lines start with a -. Also here I think it matters most to stick to one method.
But the whole big question is: should we stick to SRT? Yes, it is simple, and it's his strength, and I like its simplicity. But sometimes I feel I need something more. I'd like to be able to set subtitle position. It's something that you don't change every 10 seconds. But it's really difficult to read the subtitles when there are credit lines in the image.
I think: Subtitles is text and timing and SRT supports that, that's enough. I have my VLC player set up to use a nice font, nice size, nice position and enough shade to be visible on any background.
And then you start seeing those <i> and <b> in SRTs, without any guarantee that they are effective. And then you start wondering what can be put in an SRT: What about "<font>" or "<u>"? And the answer is that you put whatever you want and the software interprets them as it wants. Not a very good system. Most of the time what they mean with "<i>" is "out of picture". Then, why don't you say it? Why has it to be in italics?
I use italics for 'out of view', spoken text on tv, incidental foreign or alien words, or not at all. It involves a risk, but so be it, I think the risk is small enough to pay for the added value.
I avoid <font> and <u> and that kind of formatting, even though the risk might be as small as with <i>. Underlining decreases readability and emphasis and meaning could (should) be achieved with writing good text. Coloring fonts could be helpful for HI subs (Zed's text is yellow, Harry's text is green), but given the risk, maybe this is the wrong way to make HI subs.