Update 5 September 2019. The CJEU today has confirmed. See at 44 for the forum non issue.
Szpunar AG Opined in C-468/18 R v P that in the absence of formal provisions to that effect, the Maintenance Regulation 4/2009 cannot be interpreted to include a forum non conveniens rule.
The referring court is asking, in essence, whether Article 3(a) and Article 5 of Regulation 4/2009 must be interpreted as meaning that they preclude a court of a Member State with jurisdiction to hear an action relating to a maintenance obligation brought against a defendant who is habitually resident in that Member State or who has entered an appearance before that court from declining to exercise that jurisdiction on the grounds that such a claim is ancillary to a claim relating to parental responsibility, within the meaning of Article 3(d) of that regulation, and that the court with jurisdiction to hear the latter claim would be better placed, having regard to the best interests of the child, to adjudicate on those claims.
The Court’s first Advocate-General clearly and succinctly lays out the relevant principles and reference is best made to the Opinion. It is particularly at 83, including in relevant footnote, that he points out the consequences of the EU’s approach to distribution of jurisdiction: unless a Regulation (such as in Brussels IIa; or now also Brussels Ia) includes a forum non rule, forum non must not apply.