This is a plugin API discussion about a java method to spawn clothing items in a player's inventory. Please keep suggestions in the suggestions or discussions sections of the forum as not many people read the Java API part of the forum that is mainly addressed to plugin developers
to partly answer your question thought: a few new clothing items are added with every update so I am pretty sure other types of clothing like the ones you mention are in the works.
I was actually speaking of adding it as an addon by users rather than created by the devs. Somewhere we can put files and such for our own designed clothing. I would presume this comes under the remit of a clothing addon for the API.
oh I see, no no this method or the API in general cannot add new (not already existing in the game) items, clothing, objects or anything else.
What you describe is actually planned but it is not clear yet if it will be under the Java API or Modding (i.e. no coding involved just adding files to the game's files) which will most likely be realised through the steam workshop
No worries and yes unfortunately in the game's current state the only way to "mod" it is by extracting files out of the .jar archives, editing them, and then repacking them in the .jar archive they came from.
Modding in the way you describe above is the easiest and most common way to go, at least judging from experience with other games.
Having said that you can change the base block textures by adding a custom texture pack. The way for you to do that is by creating your texture pack and then adding the path to it in the config.properties file under this setting: "custom_texturepack=PATH_TO_CUSTOM_TEXTURE_PACK"
There is this german tutorial (which I should sit and translate to english at some point ) on how to set up a texture pack: Eigenes Texturepack erstellen , hopefully with the help of google translate you can use it for now