Nether Portal, exit and entry only portals

Nether portal linking and be an interesting challenge, and when working with multiple portals in a confided area can make it difficult to integrate into an existing large, multi-tiered base. 

Adding a little extra functionality could be useful, without changing too much and feeling the Minecraft feel. Making the floor of the portal crying obsidian would make an entry only portal, when entering the portal, it would behave as normal, but when you are returning, this would not read as a valid portal and the game would look for a valid portal, and if not found, create one as normal. 
Making the roof of the portal crying obsidian would make an exit only portal, would not work when entering the portal, but will be read as a valid receiving portal. 
Same calculations would apply, if two exit only portals are in range the closest would be used.