Definitely best of 5 for me, it is the thing that sets it apart along with the slams from the rest of the ATP tour. I don't think the other tournaments/ATP schedulers like it and are generally crowding it out, it is a fantastic development tool for all, even the countries with lots of pros. Does it need the top players, yes and no, until they have won it, most want to tick it off, ie most elite players see it as having legacy value others just love it and being part of a team. Personally I would play it alternate years always missing the Olympic years and keep the format.

Alternatively a tennis World Cup take games down to 3 sets, mixed squads of 8, if all square mixed doubles decider. Each match played over 4 days, 4 singles 2 doubles first day, upto 4 singles mixed doubles decider second, match over when a team has lost, 3 points for a win, 1 point for looser in match that goes to game 13!

First week 8 groups of 4, lots of tennis going on, no days with no tennis weekend deciding ties finish Saturday.

Week 2 junior tournament starts Sunday, senior QF, SF and final. I would have it annually on a rolling rota between North America, Europe, South America and the Far East/Middle East. often taking an elite tournament (slam equivalent) to non slam countries. Spain, Argentina, UAE, China etc.... I would have qualifying on hard courts after Aussie open. Finals on clay after Miami