I would argue that URI scheme must be as simple as possible and all data must be represented in a way which is bit machine and human readable. I would also argue that "?amount=20.3X8&label=Luke-Jr" is not easily human readable.
This syntax is really awful... and the amount format... no comment.
We don't need such a complicated one... I only see it as an ego valorization for the creators.
Adding variable names in uri : why not, if we need to extend the rfc later (for example, if comments are not included in the blockchain but manageable by a bitcoin plugin, we would need a way to say it to the bitcoin client. We may need to add a server name too), it will be needed.
bitcoin:// or bitcoin:
- bitcoin:// : more readable by humain (better separation)
- bitcoin: : used for mailto:, more standard
So, should we prefer a more readable syntax or a more standard one ? (excepting for the amount, i insist...)