In theory with the new format GB could win the Fed Cup which they could not do under the old format.
That's a very good point. We'll have as much chance of winning it as a pig flying past my window, but yes, come February, there will be 20 nations (including GB) who could win the whole thing 2 months later, whereas we would still be a very long way in the old format. But someone like Canada, who would have been at the same stage as us without the changes, might be thinking Andreescu could beat both Bencic and Teichmann/Golubic/Baczinsky/ in their play off tie to claim 2 rubbers and she and recent Wimbledon WD finalist Dabrowski (and doubles #11) could potentially team up to claim the deciding rubber, book their place in Hungary, and hope to repeat the same over there. Whereas they'd be so far away with all this World Group II playoff stuff and would needed to have gone on a 2 year tear, and Andreescu missing one tie (like she did in their most recent defeat) and it's just about curtains.
You can win these team events if you have 1 great player and a good doubles team. Although it is in a bygone era Sweden won the Davis Cup in 1975 winning 6 ties with Bjorn Borg always guaranteeing 2 singles wins and somehow getting the 3rd win mostly from the doubles. As far as the present day is concerned I don't know why Judy Murray and Anne K. wanted a change of format. There was a reason why GB spent 26 years in the lower echelons and it wasn't because there was something wrong with the format. Back in 2015 we couldn't even beat Turkey and against Belarus Jo produced one of the worst matches of career. Mind you since then Jo has played some great matches. It remains to be seen if the new event is a commercial success. It should surely be held in a country which would have qualified on merit not somewhere without any players in the top 100.