Hi!
My first post here, hope I'm following the right conventions.
I had this humble idea for a while, so I thought to go ahead and propose
it.

BIP: XX
Title: URI scheme for Blockchain exploration
Author: Marco Pontello
Status: Draft
Type: Standards Track
Created: 29 August 2015

Abstract
========
This BIP propose a simple URI scheme for looking up blocks, transactions,
addresses on a Blockchain explorer.

Motivation
==========
The purpose of this URI scheme is to enable users to handle all the
requests for details about blocks, transactions, etc. with their preferred
tool (being that a web service or a local application).

Currently a Bitcoin client usually point to an arbitrary blockchain
explorer when the user look for the details of a transaction (es. Bitcoin
Wallet use BitEasy, Mycelium or Electrum use Blockchain.info, etc.).
Other times resorting to cut&paste is needed.
The same happens with posts and messages that reference some particular
txs or blocks, if they provide links at all.

Specification
=============
The URI follow this simple form:

blockchain: <hash/string>

Examples:

blockchain:00000000000000001003e880d500968d51157f210c632e08a652af3576600198
blockchain:001949
blockchain:3b95a766d7a99b87188d6875c8484cb2b310b78459b7816d4dfc3f0f7e04281a

Rationale
=========
I thought about using some more complex scheme, or adding qualifiers to
distinguish blocks from txs, but in the end I think that keeping it simple
should be practical enough. Blockchain explorers can apply the same
disambiguation rules they are already using to process the usual search
box.

From the point of view of a wallet developer (or other tool that need to
show any kind of Blockchain references), using this scheme mean that he
can simply make it a blockchain: link and be done with it, without having
to worry about any specific Blockchain explorer or provide a means for the
user to select one.

Blockchain explorers in turn will simply offer to handle the blockchain:
URI, the first time the user visit their website, or launch/install the
application, or even set themselves if there isn't already one.

Users get the convenience of using always their preferred explorer, which
can be especially handy on mobile devices, where juggling with cut&paste
is far from ideal.