Of the three Legendary beasts, Raikou would probably be able to put Sheer Force to the best use. Thunderbolt (or Thunder in rain) coming off an equivalent of 165 Special Attack is going to absolutely tear into anything that doesn't resist it. SubCM would be even more terrifying, since Raikou has the bulk to set up on a lot of threats while still packing a lot of power.
Suicune wouldn't get as much mileage out of Sheer Force, with no-burn Scald barely out-damaging Surf. In most cases it would be better off sticking to its defensive role with Pressure.
What if any Rapid Spin user got Scrappy? (you wish :P)
What if Flygon got Tinted Lens?
As for spinners getting Scrappy, I think most of them would prefer the abilities they already use on spinning sets, barring the hitmon family (again, that's been mentioned already, imagine Hitmonlee/top firing off Hi Jump Kicks with Impunity). For example, Forretress would generally prefer Sturdy, and Starmie would prefer natural cure any day. Cloyster might be a toss-up, but 9 times out of 10, it'll enjoys it's ability to fire off BP 115-125 Icicle Spears (accounting for Multiscale in the first number) way too much to exchange it for perfect spinning. It might be an interesting niche, but most possible spinners generally have more usable abilities.
And Sturdy Shedinja actually needs a lot of support to use, atleast a spinner, something to rub off weather, something clear out Pokemon with Will-o-Wisp and Toxic....
Its commonly used in Hackmons, but it can be easily countered.
True, but if the opponent doesn't use entry hazards, damaging weather, or status causing moves, then Shed could easily sweep. It's definatly high risk, high reward. I've actually seen a few guys who are just Sturdinja bait.
As for Technician Marowak, the only major move that would boost is Bonemerang. Well that gives it higher power than EQ at least. It will still need priority to compete with Technician users like Scizor and Breloom.
Say, what if Hydreigon had Sheer Force?
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What if U-Turn had just 10 less base power? If it had only 60 base power, Scizor could wreak some serious havoc.
What if Raichu could also use the Light Ball?
What if Zekrom had Fusion Flare and Reshiram had Fusion Bolt?
Much love to Zurr
At any rate, with current Stat distributions, they probably wouldn't use either mive in sets as often. It might make a fun gimmick, but I don't see them getting the same amount of use, even if typing was switched to give stab, they would then have better options for STAB, like Reshiram would enjoy firing off Thunders a lot more, and Zekrom would enjoy flare blitz or fire punch. (note that I'm saying this under the idea that if types were swapped for STAB, and they were given moves like Thunder or Flare Blitz in their movepool, since that would be logical, as every electric type gets either Thunder or Discharge, as well as keeping their stat distribution the same)