I think Kirby mostly meant that the long delay on C isn't a sign that big things are coming, but rather a sign that NOTHING is happening for the most part. Not new additions nor bugfixes nor speed enhancements.
To be clear on my timetable I gave: I ALWAYS tweak the code to be faster/better while I am working on other things. It is while doing those tweaks that I realized how I can speed things up to a (possibly) great extent. Some of that work I can do piecemeal, and I most likely shall while writing code, but lots of it would be an INSANE drudgery and lots of repitition. The timetable of a full year accounts for me getting massively bored with the whole process and stopping for a long time, but optimistically has me coming back to it repeatedly and finishing the entire thing.
Additionally, all of this code re-write would focus on areas of the code I am already quite familiar with, and might completely miss gigantic slowdowns in sections of the code which I haven't been to yet. New features aren't generally a "Look what I can do!" event, they are more of a "What is in this file? Ooh, this could be done so much better if..." type of situation. Or a "You know, this aspect of the game is completely lacking, and would handle better for the AI/faster for the humans if we..." This second one is what led to my concept of the Aspects system for controlling changes to tiles in the same manner as we control changes to units (Promotions) or cities (Buildings)
Also note that a lot of the "unfinished additions" which people sometimes complain about or highlight when comparing mods are actually just pieces of a much larger code overhaul, and it is being done in parts because it is either a massive rewrite with lots of potential bugs to check out, or it is an in-depth new concept which takes time to implement with AI support. These get stuck at partial completion when unexpected complications arise, or other issues become critical.
So yes: From a non-Coder perspective you can say "Just stop doing anything new and make the current stuff work," but for most coders I would hope it is obvious that making stuff work REQUIRES new additions in 85% of cases, especially when the reason it doesn't work is because it is only partially implemented. And from a realistic perspective: I code to make an enjoyable game (I want it to work), but I also code to learn how to code (I want to push myself). And as with everyone in the world, where I devote freetime depends on what inspires me, so when I see potential for a nice new feature, it is near impossible NOT to add it.