The preview window in chat is very distracating. For short messages there are two places things are changing as I type and my eye gets confused which to focus on. For longer messages the height of everything jumping around just adds more confusion.
I think previews make sense for posts where there is a lot of visual separation and potentially a lot of formatting. For chat I don't really find it useful at all. Markdown formatting typically used in chat is minimal enough and simple enough to "shoot from the hip" anyway.
I would like an option in my profile (or wherever) to completely disable the feature and not show the pane at all. Less clutter, less jittery movement.
Chat message preview was added based on user feedback and has been very well recieved.
Please don't take it away.
Making it an option in the profile seems sensible if it is not too much work.
There might be a thousand other things you want to do first.
As an alternative suggestion to a per-user option (on the profile page), it might be nice to have a keyboard shortcut that toggles the preview on or off (ctrl + p comes to mind, but that's already used for printing in most browsers - but who prints anything these days :P).
This way you could quickly toggle it on, to see how a message with complicated markdown renders for example, but otherwise it is dismissed.
This toggle could be "remembered" in the browser session without needing to be a persistent user profile option.
Possibly related: I would like more room for message entry. I know that as I type more the box expands, but that causes things to move around (worse with the preview) too. I'd really like to have a box that's a few lines high right from the start, which also gives me the benefit of not having to look at the *very bottom right* of my browser to type at all. (This is one of the less-comfortable places to focus, at least for me -- though I think I've seen research supporting the claim that it's a weaker zone in general.)
This won't be _quite_ as easy as just adding `display: none;` to the element (or I would do it myself in a user style) because the same pane is re-used to show one bit of information that is functionally useful: who if anybody is getting pinged by the message.