My definition of "risky abilities" is different than I have seen others mention. I mean "risky abilities" in terms that choosing to put Ability 1 on your pokemon makes it somewhat "opposed" to choosing Ability 2. So you, as a team builder, make a conscious choice that is somewhat risky. Obviously all pokemon with two viable abilities force you to make a choice, but I'm referring to a fairly specific pairing of abilities.
The closest example I can find off the top of my head is Bronzong. You choose to address Zong's fire weakness or its ground weakness, but you can't get both and there is "risk" in making that choice, depending on how you want Zong to play. Now, in reality we know that Zong is always Levitate, because immunity to Ground is a lot better than reduced damage to Fire. But hopefully you get where I am going, in terms of "opposing abilities" and "risk".
I see Porygon-Z as having kinda the same "risky choice ability pair" with Adaptability and Download. You choose to increase STAB or increase your attacking stat, with a clear tradeoff, but the tradeoff is confined to a specific "theme". In PoryZ's case, it is "attacking boosts". With Bronzong it is "defensive weakness mitigation". The abilities have synergy, and they have a somewhat risky choice. Whereas most other pokemon may have unreliable or high-risk-reward abilities, but that's not the same as trying to give two synergistic abilities that require a risky choice in team building.
If we wanted to try and give this pokemon a "risky pair" of abilities as I mention above, then we probably can't do that with the normal CAP process. Because normal CAP process picks one ability from a slate of choices, then the second ability is picked from another slate. It would be practically impossible to end up with synergy between both abilities, at the level I am talking about. We would have to pick the abilities as a pair, kinda like we pick Typing as a pair now. (For you newer CAP members, we used to pick typing in two separate steps)
Anyway, I'm just throwing out there the concept of ability risk in terms of teambuilding, and not just the ability mechanics by itself. Because you could have two abilities, that by themselves don't have any real risk, but when paired with the right other ability, could present an intriguing risk-reward proposition to the team builder.