With the launch of 1.18beta on Steam the MP4 has now been released. As a result the F1 Combo pack now has Mercedes and Williams added to it with the MP4 Stobart Mercs. These can also be found as solo packs for those who just want specific skins.
For those not paying attention update 1.18 beta is out on Steam.
The templates file has been updated for the MP4.
You can temporarily download just the MP4 templates here.