The Olympics has a massive place in the history of football. It predates the football world cup as the first global tournament between the top national teams in the world but eventually the world cup took over to the point that the Olympics is now an afterthought for most football fans. With only 3 over 23 year olds allowed, you don't see the top players competing and I don't know if the tournament benefits anybody at the moment especially as footballers are already tied up playing too many matches.
Futsal on the other hand is an amazing sport that could really do with a global spotlight. It contains extremely talented players that any football fan can appreciate. Most fans of football have either played futsal or it's close cousin, 5 a side/7 a side football.
In rugby, they don't have the more popular rugby union or rugby league at the Olympic Games, they instead have the niche sport of rugby 7s and it rocks. It's the highlight of the rugby 7s calendar and the shorter form of the game is much easier to watch for casuals. In addition to this a handful of the top players in rugby union such as likely the best player in the world, Antoine Dupont is joining the national 7s team for the Olympics which just adds to the buzz. It's a different sport but similar enough that there's so much curiosity among fans.
Imagine an Olympic final with a futsal team led by Lionel Messi. Tell me you guys wouldn't want to watch that!
The shorter format also means that the tournaments can be much quicker and the players wont get worn out like with 11 a side. I think it would benefit not just futsal but football as well.