The Commission won't like anything that interferes with its right of initiative. The only thing in the wording you could take against obliging the Commission is that it says 'invite'. And the right of initiative is only written down in the Treaty on European Union as follows:

Union legislative acts may only be adopted on the basis of a Commission proposal, except
where the Treaties provide otherwise.

There's no clear precedent I can think of...

A text by democracy international (pdf) (google viewer) states the following:

It is imperative that the legal nature of the ECI is initially defined. The ECI allows citizens to ask (or "invite") the Commission to start a legislative process. This wording leaves open the legal nature of the ECI. It has already created some confusion among analysts of ECI regarding the role of the European Commission.

It is quite clear that the ECI is non-binding for the Commission in the sense that it has to submit the ECI proposal unchanged to the Parliament and the Council. This would not be in line with the Commission's monopoly of legislative initiative and the wording of Art. 11 (4). However according to the majority view of European law experts and the "effet utile" of the ECI, it has a binding nature for the Commission in the sense that it has to take some legislative action on the topic proposed by the ECI. The precondition is that the ECI is declared admissible.

The text goes on to draw an analogy to the indirect right of initiative of the European Parliament and the Council under the old EC Treaties, which could be used as precedents for the degree to which the Commission would be restricted.

I agree with pushing for an obligation of the Commission to initiate legislation on the topic of the initiative and in the sense of the initiative.