I'm not saying this to downplay the project (I know very little about it) but the reception among those in the field it's supposedly applicable for has been underwhelming.
The real breakthroughs that I was talking about are for time resolved and "diffract before destroy" experiments for delicate samples. Those ones can't really be done at a synchrotron with long bunches.
I'm especially excited for femtosecond time resolved measurements of chemical reactions. It's going to be so cool to watch chemical reactions occur at an atomic scale.
I guess the other cool application is that there is so much light that you can perform diffraction off of single molecules when you want your sample in solution/gas phase or can't form crystals. Correct me if I'm wrong, but my impression was that the intensity of XFELs also enabled that.
The way that the project is being sold from the structural side is that you won't need a crystal, which is obviously huge. However, there's the issue of scale, and also the classic issue of... We can't refocus diffracted X rays so we're still limited by protein we can express in a selenium doped media, since you need the selenium signal to determine phase data from the diffractions. The list of proteins that are soluble but won't crystallize/can't be resolved by Cryo-EM is pretty small, and so it's an incremental upgrade no one will have access to, at best. At least, from the structural side.