EPSG has added it as 6647.
At Esri, I have it in a development build, but it's not in ArcGIS 10.3 (hopefully 10.3.1). Here's the Esri WKT for it:
This document on height modernization (1.36 MB) from Service New Brunswick shows differences from CGVD28 of +0.55 m in Banff to -0.64 m in Halifax. I would call those differences significant for more than high-end surveying work.
If you (as a GIS person) receive CGVD13 data, you'll want to make sure the metadata reflects that. Also, as it's now the official vertical coordinate reference system, government agencies may start requiring that vertical data use CGVD2013.
EDIT: How to incorporate the new definition
Esri removed the "Coordinate Systems" folder and its thousands of prj files at version 10.0. People used to drop in custom definitions there or move things around. If you're using a 10.0 or later version:
Keep custom prj files in a directory to which you have a folder connection. Then when choosing a coordinate system, you can use the "import" option to browse to that folder and pick a prj file.
(Tip: use "add to Favorites" context menu, which is a shortcut for copying prj files in the ArcGIS "Favorites" location,
C:\Users\your_login\AppData\Roaming\ESRI\Desktop10.X\ArcMap\Coordinate Systems in Windows 7; replace Desktop10.x with your major release version (10.0 / 10.1 / etc.).)
The coordinate systems "picker" is smart enough that a vertical coordinate system prj file will not show up in ArcMap data frame properties' Coordinate System tab, but is available if you're using Define Projection Tool, or a data's property page in ArcCatalog.
(* You did get the name of someone who studies and practices geodesy correct!)