Neither of them has seen all that much formal testing, but that's mainly because both are foregone conclusions due to their defensive prowess.
The current list of things I could potentially see the legality changing of are:
1. Metal Fury Scythe - this is practically an inevitability, as even if it isn't completely gamebreaking due to requiring some skill to use to beat a suitably large range of combinations, it is definitely bad for the format's health, acting as a pseudo-RS in terms of centralising attack around a few wheels and destroying the viability of a number of interesting customizations (in particular, a few Metal Flat customs). Just a waiting game at this point.
2. Gravity - Gravity should get another shot in future, as long as Libra stays around and RDF/SA165 don't come into the picture. As it stands, while I would like to do some two-person experimentation with it, I am very much unconvinced that (MF-L) Gravity Perseus/Perseus (Stamina) F230CF/GCF is nearly as powerful as it was made out to be (it doesn't strike me as significantly more threatening than MSF-L Dark Knight Genbull, as the dual spin doesn't really help when all the relevant left spin combinations are likely going to KO it either way (or are dumb spin-steal stuff that people should probably get over because it's just not that amazing in limited tbh)). I think the call was made too quickly, particularly in terms of the data it was based on. Gravity + CF/GCF is a strong combination no doubt, but the final tournament it was legal in gave rise to a number of customizations that are very much viable counters to it (and frankly, with the amount of 145-Height Lightning Attack customs that tournament saw I kinda feel like any unconscious aversion to using it on the grounds of it being 'too strong' would have paled in significance to the aversion to using it on the grounds of doing so being a downright stupid idea), and I think after that point, assuming people in other places actually took note of that, we would quickly see usage fall down to acceptable levels.
I also feel that as gravity could make a number of otherwise useless tracks and tips viable (something it would be cool if people looked into), we should focus to a degree on getting it back into the format. My suggestion would be to change the rule on dual spin launchers in Limited so that it is no longer legal to change directions between the different rounds of a beybattle. A lot of people said gravity was 'too safe', and I think that would change that. It would definitely be a very popular wheel and show up very regularly in winning combinations lists anyway, just because even with that it is still a good buy in terms of being dual spin, but I think it would be a worthwhile step.
I will probably propose something along these lines for post-BeyDays stuff, again though that would still depend upon me doing some two-person tests and the banlist staying relatively stable.
3. Libra - I anticipate some panic when certain combos, in particular MF-H Libra CH120RF, start dominating because the meta in most places seems to have shifted to one that is ripe for the picking for it. It is maybe very slightly too good, but removing it will leave a big hole in defense which will need to be filled by something - and that something will almost certainly require a lot less skill to use. I'm hoping if I say this enough I might reduce the inevitable knee-jerk reaction that'll occur but considering the reputation the wheel holds, those hopes are not that high.
4. RS - It would be a mistake, hurting the viability of a lot of older wheels severely and overcentralizng the attack meta to a few specific wheels, particularly Lightning. But, I can still see it happening if Libra gets banned.
5. RDF - Some parties will want this unbanned instead of RS, if it comes to that. I'm incredibly uncomfortable with the idea while Metal Fury LDG roams the format, and I think it's overall a much more dangerous tip than RS - instead of overcentralizing the attack meta around Lightning, it'll wreck attack entirely (in large part because people are comfortable with using RDF), which would remove a lot of the distinctive traits that have made Limited popular.
6. SA165: If Libra goes, this could be a more reasonable buff to defense than RS and RDF, seeing as Libra SA165 was one of the main problems with unbanning it. Would need to look into how various setups fare on it, but it may be the best option in a bad situation.
The next three are a big stretch, and incredibly unlike but I mean I guess I could see it happening.
7. Metal Fury L-Drago Guardian: It doesn't seem to be a threat but IDK I just can't get over it being one of the heavier wheels in the format, and based on a wheel that was decent for defensive spin steal etc. Oh, the cores from the 4D/hyperblade LDD/LDG could possibly get the boot if the ruling on them changes or whatever but yeah.
8. Omega/Jade: Maybe their weight and decent performance against all height will make them dominate the attack meta? Personally, I don't think they're significantly more threatening than Pegasis but I could see them maybe exiting the format at a stretch.
10: Hell: it would be a really bad move and is a huge stretch to consider. Between the elevation, offensive power, weight, and stamina, Hell would be an incredibly dominant force - kinda like AA2 Scythe, maybe a little more, and with a bit less defense/pure stamina and a tonne more attack and "being a massive pain on 230", except pretty much everyone would have it. Nonetheless, I'm also not entirely sure that any one hell combination is necessarily strong enough to make that as clear as it should be - again like Scythe, I feel it falls just a little bit short in terms of putting its incredible ability in each individual type to use properly in a single combination to really properly demonstrate its ability to affect the format, and based on that I could conceivably see it being discussed.
One or two other things have been mentioned but they're either incredibly unlikely or much, much more trouble than they're worth.