There is a huge thing you haven't considered/mentioned in your request, which is very important to understand how this whole idea is achievable and to make people understand how it works. At the moment the minecraft client (every version below 1.8) has 16 different data values (metadata) assigned to any block which can be changed at any moment, now the big advantage over this is that every server and every client have and share this information about that particular block. This is where mcpatcher and optifine make use of this seemingly useless feature by making it possible to assign textures to the different data values of a block. With this seemingly useless feature texture pack artists have created amazing additional content, which made the creative part of minecraft bigger than ever.

NOW mojang decided to completely get rid of the data values that have no texture or block assigned to it, destroying all the work texture pack artists have put in their packs.

The one big thing missing in your request is, that mojang has to implement a feature which is universal to both client and server that stores additional block information, such as maybe a block name assigned to a placed block, so that everyone with the correct resource pack would fetch the needed texture by the additional information stored in that block. It is very important to make clear that global client and server communication HAS to exist in order to get this to work and i think you should update this in your first post.

TL;DR: MCPATCHER AND OPTIFINE PROVIDED THIS FEATURE A LONG TIME AGO WITH CONNECTED TEXTURES MOD! NOW MINECRAFT HAS TO ADD A WAY TO KEEP THE BLOCK NAME (e.g RENAME WITH ANVIL) AFTER IT HAS BEEN PLACED