In his Opinion of 23 January 2014 in case C-15/13 Datenlotsen Informationssysteme (not available in English), Advocate General Mengozzi advocated for an extension of the "in-house" public procurement exception beyond its current boundaries under the so-called Teckal doctrine.
The AG proposed that the CJEU declares that
A contract concerned with the provision of services which beneficiary, being a contracting authority within the meaning of Directive 2004/18, does not exercise over the entity that provides the services a control similar to that exercised over its own services, but where both entities are subject to the control of an institution that can be classified as a contracting entity within the meaning of that directive, and where both the recipient of the services and the provider thereof conduct the essential part of their activities for the institution that controls them, is a public contract to the extent that it is a written contract between the contractor and the recipient of the services, always provided that such contract has an object which would qualify as the provision of services within the meaning of the directive.
Such a contract is not entitled to an exception to the application of procurement procedures under the EU rules on public procurement unless the controlling entity exercises in an exclusive manner a control similar to that exercised over its own departments both on the beneficiary of the services and on the providing entity, and where both of those entities carry out the essential part of their activities for that controlling entity, or in the case where that contract meets all the requirements for the the exception for public-public cooperation (own translation from Spanish and French).
Therefore, AG Mengozzi suggests a test whereby, if all of the entities involved in the contract would independently qualify for the "in-house" exception in case they were engaged in a vertical contract with the ultimate controlling entity, they can then also benefit from the "public house" exception in their horizontal contractual relationships.
If the CJEU follows the approach suggested by AG Mengozzi, it will be extending the "in-house" exception beyond its current limits (where a direct control is required on the part of the contracting entity over the awardee of the contract) and creating a "public house" exception in public procurement--which was anticipated and discussed by Dario Casalini, 'Beyond EU Law: the New "Public House"', in Risvig Hansen et al (eds), EU Procurement Directives--modernisation, growth & innovation (Copenhagen, DJOF, 2012) 151-178.
It is also interesting to stress that such "public house" exception has also been created for the future by the new Public Procurement Directive (bound to be transposed by early 2016), which article 12(2) frames it in slightly different terms, indicating that the "in-house" exception:
also applies where a controlled legal person which is a contracting authority awards a contract to its controlling contracting authority, or to another legal person controlled by the same contracting authority, provided that there is no direct private capital participation in the legal person being awarded the public contract with the exception of non-controlling and non-blocking forms of private capital participation required by national legislative provisions, in conformity with the Treaties, which do not exert a decisive influence on the controlled legal person (emphasis added).
It is important to stress that the requirements concerning private capital participation deviate from the standard "in-house" exception and (if adopted) from the "public house" exception, which may create some interpretative difficulties in the future. For now, I guess we need to wait and first see if the CJEU supports the "public house" exception as a first step, before worrying about the confines of a (private)-public house exception...