While your concern about the engine is right, it appears that Paradox made a very deliberate decision to remove Fuel from the game. I would be suprised, not that it won't happen, but I would be very surprised if Paradox did a 180, added Fuel and tacitly admitted they failed to build the game they wanted at launch after all the delays.My guess is that Paradox will devote some time to bug fixing for a month after release while at the same time podcat will work on a new DLC that should be ready around Christmas. And, if the engine is not completely unfit, one thing that is going to change is the oil issue which makes the game (in my opinion) broken.
IF I am right you should wait until September and maybe beyond.
I think the game as published will need some polish, but likely be a very 'fun' game. I'm not suggesting that any mod team will magically fix a 'broken' product and do what they couldn't do. I expect the engine to handdle adding crap like Fuel etc, even if it isn't graceful. The #1 challenge in my mind is how to train the AI to cope with something like Fuel and variable equipment attrition rates.
I have a plan for game balance vs stockpiling, but that hinges on the guts of the engine of course. I have no plan how to teach the AI to pick a strategy, form an economic plan to achive that strategy, and still react well to global events.
I cannot speak for others, but my summer in terms of modding effort would be entirely devopted to understanding the AI and mapping it's algorithms. Work on 'new' things would be months out. I'm hopping others will start in their areas of interest mapping the other parts of the engine so we can properly reverse engineer it before starting on new modules etc.
The level of complexity demands building both a requirements and interface document as well as maintaining a proper set of documentation for the various modules, both in engine and as part of the mods.
Hope this clarifies things a bit.