Yep, I see what you mean. Well, my point is that anyone who wants to start their own set should be ready to actually do some drawing of their own

I think the main point here is not much whether we can cooperate or not, but what we could achieve. I've never been against working with other artists or for other sets; I got to learn quite a lot from those experiences. Also, I felt my work was useful to the completion of other sets. One of the most fun projects I undertook was drawing the Dutch steamers. I learnt a lot about trains from that country, and that helped the Dutch trainset to be released earlier. So should a similar opportunity happen again in the future, I'd seriously consider it.
In this specific case... well, I've been working on the French set for quite a long time and, as I'm learning the joys and pains (more of the latter, actually

I know this might take a long time

In my first baby steps as a coder, I'm realizing how complex it is to code a set like the French one, with all the cross-dependencies I have planned between locomotives and wagons. There are many possible matches, depending on year of built, companies chosen, special conditions if any, and many more conditions, and they all lead to more or less different graphical or functional effects. Even coding a relatively simple chunk of the French set, as the narrow gauge section is, involves a lot of attention and a thorough planning to make everything work as intended.
For this reason, all of my graphics is drawn with coding in mind.
The French set will have so many cross-dependencies, that sharing the same code with another set would be totally out of question. Not because of copyright issues; because of practical reasons. Even something like a 2cc-colored French set would not use any of the dependencies the original French set has; it will use others instead. I believe it would be more practical to start a 2cc French set from scratch, as, to my understanding, you guys are doing.
If your aim is to put together all available graphics and develop a set with French trains as quickly as possible, I of course will never stop you

By the way, why dropping the steamers from the set altogether? They're not so hard to draw as they might seem, and they give a lot of experience and satisfaction. Also, if you limit your set to SNCF rolling stock, you'll start from 1938 and you won't have to draw too many of them anyway.
If you still think about including some already-drawn sprites, well, I'm not the only one around this forum who drew French steamers. Hovering Teacup made quite a few, years ago; we originally planned to include them into the French set, but we eventually won't. Also, Singaporekid once drew a quite nice 242A. Those sprites must be buried somewhere in the early pages of the French set thread. Since they will not be included, you can definitely use them after asking permission for them.