Who cares? The game is stuffed with alts already anyway. CCP deliberately encouages alts and always has.
“Exploitable” generally means ‘exploiting’ some game mechanic for measurable gain. In this concept, CCP would be adding an expense/ISK sink and then using corp member count to reduce the cost of the ISK sink. No benefit is gained, it’s still an ISK sink that doesn’t currently exist.
A decent coder could set it up so that only active members count, or other limits. But even without limitations on alt-activity, some people will use alts, some will recruit members, who cares? An approach doesn’t have to be ‘perfect’ to be beneficial.
The “fleet together” idea you also say “exploitable with alts” to. Again, who cares? Using other alts in a fleet means you are either paying Omega for all those alts, or you are using trickery to get around Alpha limitations (a very limited portion of the player base). For 90% of players it will be an incentive to either Omega multiple accounts or fleet up with other people.
Here’s a scenario: CCP implements a slightly modified new Triglavian mechanic. A “Triglavian Conduit” beacon opens in a system. People warp to it, it has a Concord ship there which carries special “Conduit filaments”. The ship dialog says you need 3, 5 or 7 Conduit filaments to open a warp tunnel into the conduit. You slap together a fleet of (at least) 3, 5 or 7 ships, each ship buys a filament from the Concord ship (this is an ‘actively present’ check as well as an ISK sink), they activate them, Conduit opens, they jump in.
Goal is to destroy 3, 6 or 9 structures inside, while fighting the defenders, before the Conduit activates. Failure, no payment. Success, a new “Concord Scramble Alert” type of LP is paid to the whole fleet. 70% of the payout (depending on 3/5/7 size) is divided between the fleet evenly. 20% goes to the top DPS. 10% to the second highest.
Scramble Alert stores trade LP for packages of ISK, SP, or Standings boosters. Also, a more expensive ‘random’ box that can award the above, or Triglav salvage, Cerebral accelerators, skins, whatever.
Now you have a mechanic, that is basically a few tweaks on existing mechanics, that introduces multiple benefits (ISK sinks, players fleeting together, new content, new rewards, ‘random’ boxes). At that point it is irrelevant if some people use alts to do it - the benefits far outweigh any alt abuse.
The biggest benefit in my eyes though, is that now you have a mechanic that is only one step away from “make two fleets, jump them in and have them engage in competitive struggle/PvP for a goal”. Which is what (IMO) ‘Resource Wars’ always should have been.