There are various terms for "end-site" in the IPv6 allocation and assignment policy and the RFC 3177. We need to have a finally definition for "end-site" to establish clear internal assignment policies.
a. Arguments supporting the proposal
At last we will have a concrete definition for end-site. There are a lot of discussions even in different RIR regions and as far as i know non of this has reached an conclusion.
The RFC 3177 defines end site as single edge networks, this is pretty close to my proposal and i think it is easier to update a RIPE Policy than an rfc.
This question was discussed in the IPv6 maillist before and it looks like that this definition could get a majority approval.
In the IPv6 End User Site Assignment Request Form (ripe-308) the requester has to confirm that he read the policy document. It is hard for a customer to understand these improper terms.
This proposal should not be combined with the /48 /56 discussion which is on at the moment. It´s just a matter of definition
b. Arguments opposing the proposal
I can´t see anything against this ...