Nah Kyogre and Groudon's would be nerfed too since it's the same ability.
Also since weather wouldn't be permanent, would that make Excadrill go back down to OU since the Sandstorm wouldn't be endless and thus lose all of it's Speed when it wears off? It would also mean Drizzle + Swift Swim is legal again since it's not endless rain. Man this will affect the tiers big time if it happened.
Oh and I've said this before elsewhere but I reckon the Rotom Formes should get the whole Kyurem treatment and get their own individual movepool and when they forme change, their moveset resets. (Kyurem-W gets Fusion Flare and Ice Burn while Kyurem-B gets Fusion Bolt and Freeze Shock at Lv43 and 50 respectively and they lose them when it goes back to Kyurem) But unlike the Kyurem formes, they also learn different TM/HM/Tutor moves.
For example. Let's say Rotom-W learns TM55 Scald. When it changes forme, it loses Scald and all moves it had and resets the moveset to match the latest level up moves at the current level of that forme. Another example is Rotom-S learning Hurricane.
Also they should all get a 2nd ability that fits them perfectly: Motor Drive! Rotom is Motor backwards and well you know. lol
With Hurricane and Motor Drive, Rotom-S would actually be usable.