A good target for regulation for those clouds would be the inflated traffic pricing.

Either by a simple price limit on ordinary egress (e.g. max 1 EUR / TB to European providers which don't charge for peering/traffic), or by requiring them to peer at-cost with others and allowing the customers to choose such a peering for egress.

The current traffic pricing is extremely high, and makes it difficult to split your cloud installation between multiple providers.