This came to mind while reading another post about Rival opponents and their ability (or inability) to take strain as wounds damage.

In the case of a lightsaber-wielding Rival, what would become of the Parry and Reflect abilities that trade wounds for strain?

This is mainly an hypothetical question as a lightsaber-wielding opponent would likely be a Nemesis opponent.

I would say that, if worths it, Rival can use it. A Rival would take 3 damage to Wounds to prevent even more, If the damage is less than 3 then, let it pass

We haven't seen it yet. Though as Josep pointed out, it poses the same conundrum as a reflecting a stun blast or parrying a weapon that deals stun damage. If the stun (wounds) the rival would take is greater than the 3 + remaining stun damage, then there isn't really a problem.

Despite that, as general design principal, I would argue that any NPC statted to use stun and parry, should probably be a nemesis, even if they aren't the BBEG or "mid boss"

This came to mind while reading another post about Rival opponents and their ability (or inability) to take strain as wounds damage.

In the case of a lightsaber-wielding Rival, what would become of the Parry and Reflect abilities that trade wounds for strain?

You would track their strain. The book says "GMs can decide to track strain on certain rivals, even though this is not the norm. This does create extra bookkeeping for the GM, but it also allows some additional granularity for rivals who might prove important to teh plot. In essence, this allows the gm to create nemesis class characters with weaker than average stats."

I've used Parry/Reflect for fairly specific Rivals, namely adversaries that I wanted to be a challenge to the PCs (especially the lightsaber-using crowd) but not a major recurring threat. Alhough mathematically it's really only a boon to the Rival if they've got 3 or more ranks in said talent.