One of the most common sights in Overwatch's competitive games is the 2-2-2 team composition. Consisting of (as the name implies) two damage dealing characters, two tanks, and two healers, it is widely regarded as one of the most versatile ways to organize your team. Of the (soon to be 23) heroes in the game, you can almost guarantee that thanks to this widely known strategy, you will likely see at least one Reinhardt, Zarya, Lucio, Zenyatta or Ana, McCree, and a skirmisher like Reaper or Tracer per game. With the inevitable release of Sombra and her ability to interrupt pretty much every other ability in the game, however, teams may need to consider using other, slightly less popular heroes.
A brief look at Sombra's abilities (which can be seen here) would tell you that she is obviously well-equipped for skirmishing. Much like Tracer, she has to get behind the enemy team (or at least get very close to them) to be able to do any real damage, although Sombra has a higher emphasis on disrupting the other team than forcing them to break formation. Her Hack ability essentially interrupts and prevents any other ability from being used (this includes Ultimate abilities), but she does require a couple of seconds to actually use the ability, and she can be interrupted in this short period of time. Her Ultimate ability is essentially the same thing except on steroids, affecting multiple enemies and destroying shields and barriers, making it more of a "set-up" Ult (similar to Zarya's Ultimate ability) that is rather weak on its own, but devastating when coupled with a well-coordinated team. Naturally, this means that if you see a Sombra on the other team, you must keep an eye on flanking routes, and if you have a Sombra on your team, you must be a good distraction be ready to exploit any opportunities that she creates.
This all sounds powerful in theory, so you may be wondering how will this translate over to an actual game of Overwatch. As far as healers go, Mercy would arguably be the least affected by Sombra's Hack and EMP abilities, given that her "weapon" is what heals people, not her abilities. Conversely, Lucio and Zenyatta (and to a lesser degree, Ana), would essentially become useless given that the main source of their healing comes from their abilities. Similarly, most Tanks would find themselves quite vulnerable to Hack and EMP given that their abilities are what gives them their utility, although realistically speaking it would be incredibly dangerous for Sombra to Hack any of the Tanks since they can just turn around and kill her with no real problem,assuming that someone sees her. Plus, as one can probably expect, active Barriers, such as Reinhardt and Winston's shield, prevent hacking attempts much like how Zenyatta can't Discord targets that are already protected by Barriers. Obviously, Hacking or EMPing other Attackers (and for that matter, most Defenders) can be rather useful in both offensive and defensive scenarios, functioning much like a more preemptive version of McCree's Flashbang in that you can interrupt or prevent high-damage Ultimate abilities from being used, but it may prove to be too dangerous to be worth the risk.
Given all of her limitations, though, Sombra will likely end up being a very niche Hero to pick in any Overwatch match, seeing use only if the other team is adamant on turtling behind Reinhardt's shield. While her Ultimate ability is very powerful, the fact that her effectiveness relies on both the other team being inattentive and her own team being good enough to exploit her Hacking ability means that in most cases, having a Tracer would be just as good, if not better (plus it would be rather unwise to pick a Hero solely based on how effective their Ult is). While Sombra can prevent abilities from being used for a short time, Tracer is arguably just as effective in that regard because she can simply kill other Heroes or better yet, force them to preemptively use their abilities; Sombra may be more effective against Tanks and their abilities, but Tracer is more effective against pretty much everyone else.
In the grand scheme of things, the existence of Sombra might cause teams to substitute Lucio or Zenyatta for Mercy or Tracer for Sombra if the situation demands it, but it would likely not cause as big of an effect on the rest of Overwatch's meta due to the significantly higher degree of coordination that is required from the rest of her team.