- Whenever a brand is mentioned in a text box, the text becomes the make's logo
Annoying and not really useful.
But I plan to add some day a better handling of makes, so there could be a page with info about each make (including logos).

- More emojis!
You can use all the real emojis in addition to the few smilies provided
https://emojipedia.org/

- GIFs
No. But you can embed an image from an external site...

- Whenever a link is shown, a preview of that site shows up
No, this can be a source of security issues. You can just click on it if you want to see what is behind the link

- Crossing out text
Actually this exists, there is the "strike" tag, I see that I forgot to put it in the help page I'll add it there.

- Different coloured text (excuse my spelling, I'm as British as a Bentley)
That is the kind of thing that would be quickly annoying, and often difficult to read...

Hi, I feel a sensation that BBCode needs something new. I've narrowed what could be missing into this poll, vote for whichever addition you want