Historically (Ext JS 3-) we have supported dots in the xtype of components but with the introduction to the alias throughout the frameworks this broke the usage of dots. So instead I have steered people into using underscores instead of dots which accomplishes the same things as a dot like "nesting" your xtype in a sort.
I just tested this component in Ext JS 4.1.2 and Sencha Touch 2.1.0 RC2:
And neither framework supports it currently. We do have an internal bug filed for Ext JS 4 (EXTJSIV-2577 for any other Sencha employee looking at this) and it looks like it may get fixed for 4.2.0 but it's currently an open bug ticket. So we want to support it once again and will support it but it's not a blocker bug as you can use characters like an underscore.
So Architect isn't allowing it because the frameworks don't support it currently for components. Technically things like stores and plugins use the alias like a component does but since ComponentQuery is what breaks things for components but is not used for other classes that support alias, technically dots should be valid for those classes just not for components.
// later in some other component, i.e. a container:
Works perfectly since 3.0 all through 4.1.x. I've built whole app with tens of widgets, panels, etc. and they are namespaced because of the sheer number of those. Ext Designer handled the task with no problem, while Architect refuses to digest the dot for some reason (even though after manually editing and adding the dot, all works well).
Correct but that's just half of the story. Resolving that component will not work therefore we cannot say it's fully working and can then understand why Architect does not allow for it.
This simply means we need to file a bug for CQuery, but this Architect bug still stands. As I've described above, component/container building and "Ext Designer" worked flawlessly. It's possible CQ bug has been introduced somewhere after 4.0.1.