Comments in the media revealed a plan to change the current 2015 rules in order to have one extra Power Unit allocation. Possibilities at this moment could either be to only allow this allocation during practice, or without restrictions so that teams can run them as they please.
The plan has been brought up to discussion, and received apparently full support. Christian Horner, Team Principal Red Bull Racing, brought the idea forward on a Strategic Work Group (SWG) gathering.
The change will still need approval of the WMSC before the rule change became a reality. It seems very unlikely however that the WMSC will disapprove. The next WMSC meeting is unknown at this point, but a simple tax vote would in theory suffice.
Changing current (or even 2016) rules requires unanimous support from all teams at this point, and not just the ones in the SWG. It's quite possible that the manufacturers either had to give significant price reductions on this extra, fifth engine allocation, or outright offer it for free, to convince smaller and source-limited teams like Force India and Sauber.
It would certainly help the teams who have significant reliability issues with their power units, Mclaren and the 2 Renault-powered teams specifically. We previously wrote an article about the ramifications of Renault's dire situation and how it would have them end up with taking penalties later on in the season. A 5th PU allocation without extra penalties would be a huge relief, and a chance to set things right without having to receive extra punishment.
Furthermore, it would also give extra possibilities in the sense of when manufacturers can introduce their remaining tokens. They are bound at the allocation plan of their power units, having previously only 3 moments in the season to introduce them (without a penalty) as introducing a new component spec requires the usage of a new PU component allocation. Going from 3 to 4 moments can mean a big difference.
Since most cars still are driving their first of original 4 allocations, teams can still adapt their allocation plan over the season with relative ease. This might change if it takes the WMSC too long to approve, but given the urgency put behind it is likely it will get approbated very soon.