^Well, the reason why Steel 'mons don't use Steel attacks in the current metagame, is because the current metagame works in a way that discourages it. If the metagame somehow changed so that Steel STAB suddenly became more valuable, Steel 'mons would start to use it. But it would never happen in the opposite order.
As for Pokémon that might rise to new heights in the next generation... I'd say, look at what is currently holding them back, and what could be redeemed to make the 'mon better in relation to others:
- Terrible weakness to one type (such as Charizard). Can not be redeemed unless said type gets a massive nerf. Unlikely to be fixed as generations go by, seeing as the trend has always been wider and wider movepools, including coverage moves of more and more types. Thus, more and more Pokémon will become potential counters to the one in question.
- Bad movepool (such as Kyurem-B). Can and most likely will be redeemed over the generations because more moves are added for every generation, and movepools generally become bigger.
- Bad stats (such as Ledian). Stats have never been altered since the Special stat split nearly fourteen years ago. A Pokémon suffering from bad stats is likely to stay bad, unless a mechanic addition gives it a wonderful new toy to abuse (see: Wobbuffet) or it is given an excellent new ability (see: Politoed).
- Crippled by nerf ability (such as Archeops). Not likely to be redeemed, because most Pokémon with bad abilities were made so to prevent their other qualities from making them overpowered. The only case where a Pokémon has had other abilities than its terrible one, the terrible ability was optional and given to the Pokémon after it already had got better ones (Durant). There are ways to play around terrible abilities, but generally they will remain a clamp around the Pokémon's foot.
- Generally bad ability (such as Weavile). May be redeemed if GameFreak decides to raise the number of possible abilities for each Pokémon even higher. IF the trend of more and more abilities continues, it's likely to be redeemed.
- Outclassed by another 'mon (such as Whiscash). If two or more Pokémon do mostly the same job(s), but one does everything better than the other, the "little brother" needs to gain more in a generation shift to get out of the shadow. This might include additions to movepool or abilities, but if the "big brother" also gets a similar treatment, it won't do any good. Good thing Smogon operates with several tiers.
Also, generally, making a Pokémon better wouldn't necessarily mean making it more viable. As a thought experiment, imagine if you could use a Beedrill as of BW2 in Pokémon Red and Blue. With Toxic Spikes, Drill Run, U-Turn, Venoshock, among other moves, it would absolutely rock the metagame, and throw in-game opponents around like pebbles. It would have one of the most expansive movepools ever, capable of learning techniques unheard of in its game of origin. Even Endeavor would be semi-broken on it (especially if combined with Focus Sash - after all, it would be the only Pokémon in the game capable of holding items). By R/B or even G/S standards, the current Beedrill is absolutely broken. Yet, Beedrill is still Beedrill, it has never left the lowest official tier, and still sits at the bottom of the barrel among fully evolved Pokémon. As Beedrill changed, so did everything else. All Pokémon got items, all Pokémon got abilities, and nearly everybody got big movepools. In sum, Beedrill is still nothing special.
It is, however, a heck of a lot more fun to play with than it was back in R/B. Even if some Pokémon's long sought-after additions turn out to be mediocre in the big picture, it will give it more variety for in-game and recreational purposes. I personally hope many Pokémon will get boosts, but not necessarily to make them OU material. Just more fun to play with.
Damn, it's late. I might be rambling. Better stop now.