Enterprise network as an ISP with a single huge customer

[Stepan Kucherenko <twh () megagroup ru>]

Hello,

I'm sure lots of you work for big enterprises, and some of you work for 
biggest of them.

How many of you architect your network as an ISP, with that enterprise 
as the biggest customer ? Office networks in l3vpn, VPLS/EVPN on top of 
your own network for DCI, etc ? Or is it usually just a single IGP 
domain with no unnecessary bells and whistles ?

Do you think one approach is better than the other ? If so, why ?

I understand that it usually comes down to specific circumstances and 
most likely scale but I'd still love to hear about your experience.