Discuss managing the number of ISDs and core ASes

[nicorusti]

Following discussion in scionassociation/scion-cp_I-D#42:

The ideal topology for SCION is to keep the inter-ISD core network to a moderate size, to benefit from the divide-and-conquer partitioning of ASes into ISDs and the efficiency of the intra-ISD beaconing.
What is done to ensure this? What happens if the size is not moderate? What is "moderate"?

Also, we got this feedback here :

Explain why why 4030 ISDs is enough for public addressing.

we should discuss how to keep the size inter-ISD network, the number of core ASes and ISDs moderate.