While exploring the various links provided by fellow fans, I found something that mentions the possibility of a larger-sized collector quality line: Novas coleções e dolls/New Collections and Dolls.
From what I could translate from the text written in Portuguese:
In 2015, Monster High will have a new collection … by the looks will be 'monstrinhas' in its basic version and this time with excellent quality, as every collector wants. The measures are 50cm/19inches for normal dolls, dolls 45cm for the size of Howleen and 55-60cm for the size of Nefera dolls.
What is the story behind this?