The last thing markdown needs is an alternative abstraction to build any HTML element. Once you start down that road you’re going to end up needing to deal with encoding and escaping and might as well write raw HTML. The reason markdown is so popular is that the common elements in HTML have been simplified in such a way that writing can be done quickly without having to think about such things.
It also makes the source portable and easy to digest without needing to be rendered. Once you start to make a “generic” syntax the utility quickly drops.
For example, Discourse’s own quote syntax of:
[quote="chrisalley, post:9, topic:2227"]
Perhaps a generic syntax for blocks
[/quote]
is not something I would be able to write accurately if there weren’t already quick-insert buttons in the UI. And frankly it’s ugly. I’d have preferred a dedicated syntax along the lines of:
> Perhaps a generic syntax for blocks
>
> -- @chrisalley, 2227/9
because it’s terser and easy to author without needing to rely on external automation.
So, as far as aside is concerned, I find using a generic syntax such as
:::aside
**Note:** lorem ipsum dolor sit amet.
:::
to be far too verbose and distracting where
| **Note** lorem ipsum dolor sit amet.
is clear, concise, and in-line with the similar blockquote syntax.