Will they be adding slash command support and if so, when?

[EvokerKing]

Just read the title.

[DuckMasterAl]

[EvokerKing]

So if I get the development version, how do I make it into a slash command instead of a normal one, because in the example they use !hello?

[DuckMasterAl]

That comment was about replies, not slash commands, sorry!
There is currently no information about if/when Slash Commands will be in discord.py.
However, there are some other libraries that have support for them.

[15696]

Probably not. It has a lot of limitations and would require a complete rework of the commands extension. (as said by polyjitter in issue #6149)

You can use this meanwhile:
https://github.com/Zomatree/discord.py/tree/slashcommands

[RGBCube]

It is implemented, to use it you need the development version: pip install git+https://github.com/Rapptz/discord.py