Support possibility
Okay so on the rare occasion I get a magic damage based top mid and jungle, I'd like to fall back on a physical damage support that's built for supporting. Thoughts?
Okay so on the rare occasion I get a magic damage based top mid and jungle, I'd like to fall back on a physical damage support that's built for supporting. Thoughts?

As Jon11 mentioned, there are champions built to be top lane fighters who can be seen as bot lane supports occasionally. However, I can see what you're going for: a bot lane champion that's designed to be an AD scaling support.
Now, why most supports don't scale with AD is because Riot originally didn't want supports doing loads of damage. As they seem to have embraced Brand, Zyra, and Vel'Koz support, this likely isn't the case anymore. A potential balance issue if you try to make the support actually strong without forcing them to have to buff their allies (using the AD they build) is that they could wind up being played in other roles as fighters and being a lot stronger than expected. However, I made a champion concept a while ago that does exactly that. He isn't specifically AD scaling, but he can be strong building somewhat of an AD tanky fighter build. Here is the exact concept, though there are things that I would change in it today:
En’Rak, the Void Parasite En’Rak is a champion that I designed a while ago when I wasn’t very good at concept design, so I’ve decided to rework him. His main issues were that his Q and E just felt useless, while his W and ultimate were pretty broken. Simply put, this redesign is designed to make his Q and E more useful and bring his W and R more in line. He’s designed to be this tanky parasite who enters allies, giving them his own health as a shield. The shield takes true damage and he takes full damage dealt to the shield, but with his resistances taken into account. He can also enter enemies, and has a very powerful ultimate to use this mechanic, and buff allies and debuff enemies while inside them. He also has a medium basic attack range, something like Thresh or Kled’s.
Passive: Parasitic Infestation En’Rak or the ally he’s inside of’s basic attacks apply a stacking debuff to the target. At 3 stacks, the target will take 10% more damage, deal 5% less, and En’Rak’s W can be activated on the target for 3 seconds. His W can last up to 2 seconds after the debuff fades. Allies dealing damage to the target will reapply the debuff for up to 2 seconds. In total, his W can last 7 seconds on an enemy.
Q: (unnamed) Passive: while he’s inside of an ally, that ally’s damage shreds the target’s armor and magic resistance by 2% for 4 seconds. While he’s inside of an enemy, that enemy’s armor and magic resistance are reduced by the same amount. Active: He fires out a long range glob of ooze that deals magic damage to enemies in an area and applies a stack of Parasitic Infestation to them. If you’re inside of an ally, that ally also gains attack speed.
W: Symbiosis Passive: while En’Rak is inside of an ally, that ally gains half of his health as a shield that takes true damage instead of whatever damage type was dealt to it. He takes all damage that the ally is dealt this way, reduced by the appropriate resistances. When the shield breaks, he falls off his target and he takes a burst of damage. While inside of an enemy, he steals a small amount of health per second. The damage doesn’t reapply his passive to the enemy. Active: En’Rak enters target ally or enemy champion, becoming untargetable if he’s inside of an ally. He can be inside of allies indefinitely, but can only be inside of enemies while they have 3 stacks of his passive on them. He can sling from his allies straight into another valid target or simply jump out of the target by reactivating the ability. Exiting the target will put it on cooldown, and jumping around through his teammates has a 1 second internal cooldown.
E: Parasite Swarm Passive: while inside of someone, he infests them with a swarm of parasites, giving them 4 parasites per second. Allies will shoot the parasites into the targets of their basic attacks, consuming them dealing bonus on hit damage and giving them stacks from the parasites, while enemies will simply stack them up. In the case of someone who has Runaan’s Hurricane, or Twitch, all parasites in those allies will spread to all enemies hit, giving them each all the parasites the ally had (for example, if an ally has 3 parasites in them every time they basic attack, and they have Runaan’s Hurricane to spread the shots, all 3 parasites will be applied into all 3 targets). Active: deal damage to all enemies with parasites in them based on the number of parasites and instantly detonate all parasites. Allies with parasites in them send the parasites back to En’Rak, giving him or the ally he’s inside of that number of stacks.
R: Mind Control After being inside of an enemy for at least 3 seconds, En’Rak can activate his ultimate to take control of that enemy and remain in them for the next 4 seconds. The target’s cooldowns will reset for En’Rak, including summoner spells, and will go back as they were when he took control. While inside of an enemy, the game treats that enemy as if he is on En’Rak’s team, meaning that En’Rak’s enemies can damage, cc, etc. him and he can damage, cc, etc. En’Rak’s opponents, but En’Rak’s team cannot. However, as En’Rak also controls movement, he can also force the enemy to move into a position where, as soon as the ultimate ends, his teammates can blow the target up.
Right, but what I mean is not to scale with ad exactly, but to do physical damage. I'm talking about a traditionally designed support that offers more cc or support function, reliably, than trundle or sion, and shen's abilities do magic damage, trundle only autoattacks for physical damage and sion... i find sion's cc unreliable and his passive is built for farming. Thus what I would propose is a champion, tank probably, that's abilities do flat physical damage and add support functionality in the kit, not to scale with ad, but to do physical damage. There are abilities that scale off ad that do magic damage and abilities that scale off of ap that do physical damage. What I propose is a champ that doesn't necessarily do a lot of damage, but does what damage he does as physical damage, in the instance where 3/5 people are already magic based. (this happens a lot in my low elo.) I mean, J4 can support, but he wasn't exactly designed to go bot lane support. Think braum level design support, but doing physical damage instead.