Croatia lost 3:0 against Russia. I read that seats were pretty much empty. This was mostly not the case in the old format. People cared and there was always support and feel that nations are competing for something important and bo5 format was great and doubles matches were fun to watch. Think this format will be a flop. It's just not the same when all is played in one venue in one week in bo3.
I quoted your post before, but just to update: I have looked at the website in terms of tickets. The confirmed sessions Spain was playing have been sold out since at least when the tournament started. Everything else is still available, including QFs, SFs and Fs. (Since Spain is still in, presumably they'll keep selling tickets.) But Madrid is in Europe, obviously, and there are plenty of European teams in this group. Also, Spain has a pretty sizable ex-pat community, and tennis is very popular in Spain. On top of that, Rafa, Novak and Andy all playing. So the point is, it seems hard to imagine a venue doing much better than Madrid for this new format of DC finals, and it's far from a sell-out. I'm sure DC will have to assess how well it worked out when it's over, but if Madrid loses money on it, it won't be that enticing for other cities, in future. It will be interesting to see how the new ATP tournament works out, because it's tempting to think that only one of the two will survive.