"Nasrani Mappila" is the correct term since simply "Nasrani" can lead to much confusion to readers from different countries. In many parts of the world, "Nasrani" means any Christian, especially a white (European) Christian. See this, this or this.
Simply "Syrian Christians" can refer to any Christians who follow a Syriac rite. See disambiguation page Syrian Christians. Maronites, Assyrians, etc all are Syrian Christians. There it should be either "Malabar Syrian Christians" or "Syrian Christians of Kerala". "Malankara" is also an option.
As I said on my talk page, the abbreviation is unnecessary. "'Saint' vs 'St' or 'St.' in placenames should depend upon the official usage" and "Abbreviations should be written in the same fashion each time they are used within the same page". As the main article and its forks use Saint Thomas Christians, so should this.
Readers will expect that an area titled "alternate names" on the Saint Thomas Christians template will include, well, the alternate names for that that group, not hyperdisambiguated Wiki-speak forms that are barely used. As I explained, two of the previous entries, "Malabar Syrians" and "Thomasines" are rarely if ever used. "Nasrani Mappila" is used but much less frequently than just "Nasrani". "Syrian Christians" and to a much lesser extent "Nasrani" may be confusing in other contexts, but in the Indian context in which this template in embedded, they only ever refer to the Saint Thomas Christians.--Cúchullaint/c 12:59, 22 June 2012 (UTC)
Is there anything that can be done to reduce the size of this template? It swamps many pages - eg: Varghese Payyappilly Palakkappilly - thus forcing use of galleries as a means of showing article-related images. - Sitush (talk) 14:42, 14 April 2013 (UTC)