Well, rugby is much more popular than that, in number of countries, spectators, viewership, etc.
Besides the form of rugby that is introduced in the olympics is rugby sevens, which is more widespread than rugby union itself, with a regular world series circuit and teams from every continent (except Asia maybe) playing for top spots. In the last WC the semifinalists were, for example, Kenya, Argentina, Wales and Samoa, displacing the traditional powers like Fiji, New Zealand, England, South Africa. Besides these, there's also a bunch of teams that could at any point break into a top 8 position at any competition (France, Australia, Scotland, USA, Portugal, Canada, Russia, etc.). So it's quite competitive and outspread.
You list those countries as roller hockey countries, but the truth is that maybe 1 or 2 out of 100 italians will know about it. It really is just a niche sport even in the countries that dominate it, except for 2 or 3.
Getting back at the initial question then, I think the futsal should be an olympic sport, possibly at the expenses of football itself. The men's olympic tournament is way down in the pecking order, it's only played by U23 teams. Football doesn't need the olympics for anything and the olympics shouldn't need a sport for whom the olympic games are just a 2nd rate tournament to fill in the summer schedule.
I guess otoh football, while placing expensive venue requirements (you need a bunch of big stadiums), also benefits the olympics by bringing it to other cities in the country. But for that you can have the women's tournament, who do take it seriously and for whom it is a high career mark and the best teams are sent.
Futsal otoh is a fast growing indoor sport, widely spread and which would take it seriously, benefit from it and enrich it.
