none of this would be "running" - it's just APIs, i.e. a few hundred symbols/references more
to be fair, the whole scripting-based canvas namespace is already being loaded via a so called "Nasal submodule" (based on ThorstenB's work) - IIRC, Tom adopted that in response to core developer feedback expressed on the devel list - originally, it was a conventional Nasal module in $FG_ROOT
In theory, this makes it possible to disable the Canvas modules - even though I am pretty sure that this hasn't received much attention/testing recently.
From a technical standpoint, I believe that Canvas related UI stuff would belong to the Canvas GUI module, and could also be loaded/unloaded that way.
Obviously, there is a certain grey area when it comes to modules that may also be used by non-UI work, e.g. 2D plotting on an MFD/instrument.
I do agree that core developers are likely to request Canvas APIs to be made available in an opt-in fashion, i.e. on demand.
Realistically, that's already the fact by putting stuff into the canvas namespace/module
In a way, this is not specific to this particular effort - the FG1000 also depends on certain Canvas APIs that were later (at a time when TheTom was not around), e.g. the MapStructure stuff, and we ended up loading the map APIs "always", under the assumption that such modules would not be aircraft specific, and could also be used by the UI system (which is the case).
And Stuart's FG1000 supports both use-cases, too
Equally, the Canvas/MapStructure SymbolCache texture (canvas) is currently created and populated by default, too - you can find it in every running fgfs instance by navigating the canvas tree using the property tree browser
http://wiki.flightgear.org/Canvas_MapSt ... ymbolCacheWe didn't have any well-established dependency management framework for Nasal at the time, and the addon framework also is a fairly recent development.
Thus, it would have been quite a stretch to load stuff on demand (and difficult to manage properly), i.e. premature micro-optimization that would have only provided marginal benefits