Many people are interested in things like end-to-end performance, or global connectivity. However, one must be careful how such an SLA is written. No network wants to guarantee performance or even simple connectivity to gear they do not own / control. (Well, almost no one. I know at least one company that does, but they don't sell "transit" per-se.)
Put another way, how do you write this such that my competitor cannot cause me to go bankrupt with SLA credits?
Some simple things spring to mind, such as: "Do substantially all prefixes appear in the table handed to BGP customers?" (Lawyers can fight over "substantially all". But is that really enough? Having a prefix in the table means nothing, if the path is over a cable modem in Sri Lanka. And the reverse, my prefixes appearing in other networks' tables, is under the control of my competitors.
I'm not saying it is impossible. I'm saying be careful.
Likely economic pressure is more productive, i.e. vote with your wallet. Unfortunately, on the Internet, we have a history of doing the opposite. When Sprint literally disconnected from some parts of the 'Net with ACL 112, people intentionally bought from Sprint to ensure they could reach the entire Internet. When InternetMCI couldn't connect to an exchange without packet loss to save its life, people intentionally bought from InternetMCI to avoid the congestion. Etc., etc. What did we think these networks would do when we literally paid them for their faults?
Worse, if there is a network who will not peer, and a network who will, most people buy from the non-peering network. The result of this is more networks want to close down peering, fewer want to open it up. Seems counter-productive to me, and trivially easy to fix. For instance, make peering a requirement of transit purchases. Of course, there would be other requirements (still need to run a good network, 24/7 NOC, fair pricing, yadda, yadda), but it uses financial incentives to promote the activities we want, not the opposite.
Perhaps it is time we stopped enabling - rewarding! - the very networks & behaviors most of want to change?