Ok I've had a few responses on and off list on this but arent really getting this idea, as I said tho I've not done this so perhaps thats where I'm missing the crucial points..
1) It would only remove the "must default" clause if the provider either stripped (or overrode) the local-as, or if all of the private ASNs were unique. That is a big headache.
You must strip the local-as, this is one command that can sit in a peer group on my ciscos so not a big deal.
2) Private ASNs are not, per RFC1918, supposed to be connected to the Internet, in much the same way that private IP space is not supposed to be connected to the Internet. This can also be solved by stripping/overriding.
yes
3) One advantage of using a public, albeit common, customer ASN is that if a customer has RIR-allocated space, those IPs will make it onto the global table, and will not suffer the filtering which may be present for the provider's own routes.
Ok this seems to be a difference, altho not sure why the custs IPs should need to do anything different from the providers IPs as presumably both need to be reachable from everywhere? Steve