The most useful meta data to optimize chain scan is the key birth date, then the allowed gap size. 

Tamas Blummer
http://bitsofproof.com

On 23.04.2014, at 20:39, Tier Nolan <tier.nolan@gmail.com> wrote:

> Different users could have different gap limit requirements.  20 seems very low as the default.
> 
> A merchant could easily send 20 addresses in a row to customers and none of them bother to actually buy anything.
> 
> Setting the gap limit to high is just a small extra cost in that case.
> 
> Bip-32 serialization doesn't have a way of adding meta data though.
> 
>