I see merit in this idea. However propose the uri format below:

Request Uri:
bitid:auth?bitid_address=1FZp4L1EzCtwLPZxbvopwgqBwVDzox1nxA&bitid_callback=http://example.org/login?name=Schalk

bitid_address is an optional field. If bitid_address is not provided, it will allow the user to select from multiple addresses in their BitID Mobile App repository.
bitid_callback this is a required field and is the uri called after the bitid has done it's crypto magic.

Then the request uri is called, the BitId Mobile App will append a generated a nonce (a random string), the timestamp and the bitid_address to the callback uri yielding a uri like:
http://example.org/login?name=Schalk&bitid_nonce=e15f9428-e24c-4bf5-947f-0941cd604894&bitid_timestamp=1397192899&bitid_address=1FZp4L1EzCtwLPZxbvopwgqBwVDzox1nxA

the BitId Mobile App will then sign that uri and appended the signature to the uri yielding a uri like:
http://example.org/login?name=Schalk&bitid_nonce=e15f9428-e24c-4bf5-947f-0941cd604894&bitid_timestamp=1397193115&bitid_address=1FZp4L1EzCtwLPZxbvopwgqBwVDzox1nxA&bitid_signature=HI/AuQMCo2gC49u+523oqTJDbNTDB/JbsaPZyLHmoYx83f1+fY5OU1zXAuPRD8QW7VLmrtDpKt+G1/oyBeF7+1w=

the mobile phone will then open that uri, which in the above example would open the web browser on the device, but in the case of a uri like:
cointalk:?name=Schalk&bitid_nonce=e15f9428-e24c-4bf5-947f-0941cd604894&bitid_timestamp=1397193115&bitid_address=1FZp4L1EzCtwLPZxbvopwgqBwVDzox1nxA&bitid_signature=HI/AuQMCo2gC49u+523oqTJDbNTDB/JbsaPZyLHmoYx83f1+fY5OU1zXAuPRD8QW7VLmrtDpKt+G1/oyBeF7+1w=

This would launch the CoinTalk application and log the user in.

I introduced a timestamp as then you only need to keep track of a very limited number of nonces. Depending on how the server is setup, it might only allow timestamps which are up to a minute before the timestamp in the request, this means you only have to store the nonces for the last minute. If this timestamp field wasn't there you would have to store all the nonces since the user registered and compare against them each time.