I think it's probably a good sign that they have spoken so well about the independent Long War mod. The single biggest change Long War makes *is* rebalancing the strategic layer to add some nuance and depth, although there were limits in how far they could take that building off the XCOM: EU/EW foundation. Solomon also acknowledge in a few interviews that the strategic layer was a little shallow and could probably have been improved.
So if they're making XCOM 2, they have to have taken a good hard look at revamping and expanding the strategic layer of the game. And it's Firaxis; they *do* have some institutional knowledge about strategic turn-based games to draw on.
Yes, there was only so much the long war team could do. But what they did do was amazing. I think thats why Xcom2 has been opened up to modders, because the original was'nt really (at least not at release). And that is a testament to Long Wars popularity and quality. Would be interested to know whether there is any sort of collaboration between the long war team and Firaxis. I know Solomon has mentioned them specifically and applauded their work.