Of course, you are right: it is far too late in history to make such radical changes to the rules of a sport that has been extremely successful in its present form.
But I think 3-on-3 basketball might serve as an example. It never will, and never should, replace standard 5-on-5 basketball, but it does have the potential to be an exciting sport in its own right, both to watch and to play. And obviously there is a huge overlap in skill requirements between the two flavors of basketball, so players who are good at one can easily switch over to the other. It works as an Olympic sport because some very good basketball players who just missed the 5-on-5 team can still get the Olympic experience by playing 3-on-3.
So why not have "hockey soccer" as a separate Olympic event? It could be peopled by regular soccer players who didn't quite make their national Olympic soccer team. Maybe you would have to reduce the on-court player count (say, to 6 in front of the goal keeper instead of 10), which would allow for a 3-deep roster and still stay within a team size of about 20.
And while I'm on the subject, another hockey-like rule change that you could introduce in "hockey soccer" would be an area behind the net where the ball is in play. That would open up the possibility of passes from behind the goal to a striker positioned in front of the goal, which would certainly add to the scoring. There might also be a chance for "wraparound" goals to be scored.
I would certainly watch that sport, and I think that many others (especially in Canada) would watch it also.