The game's current UI could use a serious rework - making it more compact, better readability & overall more options.
The attached images show a rough imagination of this suggestion, it is not precise pixel for pixel but should get the overall idea across.

The scoreboard for 16 players currently is very crowded and honestly very ugly. It could benefit from adding a scroll bar instead of shrinking the slots. Additionally, it could only display open & occupied slots for non-hosts. For the host specifically only 1-8 closed slot(s) should be visible. (for 16 player UI)

The loading progress should only be shown when the user is actually loading. The progress could be placed ontop of the PING counter.

Reserved slots is a small additional idea i just came up with, though still fitting for this suggestion - Only allow friends AND/OR moderators to join this slot. This may be redundant because of the Friends-only game type existing.

The badges on the bottom right of the player skin icons display if the user is a Host, Moderator, Second Player OR a BOT.

The black numbers on the top left of the user skin just indicates the slot index. Intentionally dark due to the fact it's only useful for commands & debugging.

The new buttons on the left are the Kick OR Change BOT buttons.

BOT's wins & losses should be tracked, as the empty space just looks awkward.

Interacting with the Account Name of a user brings you to their Steam Profile. Perhaps their steam profile picture could also be shown?

If spectators will ever be implemented, the spectator's dont really need any slots - Basically just show the amount of spectators at the bottom including their names.