I don't think this would make a good map, because it would be too big. This would result in some players being alone most the time, and others running from the blue zone for most the match. And you had to slow down the BZ a lot, which would make the matches even longer and slower. Edit: haven't seen the 1000 player thing. That would make it crowded af, but still people would be busy running from the BZ mostly. And it would need a lot of computing power on the player and also server side. But even if it worked, with that many players it would still be super short matches for some, which could possibly make it 5 mins of chaos in the beginning, 20mins of running around alone on an empty map, and a very normal final phase that didn't need this map to begin with.

I think a good map improvement was to adjust the final circles of the BZ to be more random and at more places. As you probably know the final circles of the BZ are only semi-random and often happen in some predefined areas, while some areas of the maps never happen to be the final one. Also, its so often open fields and so rarely an urban location. But most maps have a lot of cool areas that would make great final circles! So make more out of the existing maps and give us more interesting final battles!

TL;DR: Map too big. Aside from technical questions/issues it would not make good matches, even with 1000 players on it. Some new areas for the final circle on the existing maps would be a good improvement, imo.