The question
I have been unable to think of any real drawbacks to changing the multiclass prerequisites, but I also haven't had enough time with the 5e system to make a good judgment on that.
My question is, what are the potential problems, if any, that could arise from changing the prerequisites for multiclassing for any class?
Some background:
I have a player in my game who is playing a finesse-based paladin (he's playing a pirate who took the Oath of Vengence — a "piradin," if you will) and he rolled pretty poorly (yes, we went with rolling 4d6, drop the lowest, if you remember my previous question) on his ability scores. He stuck with his rolls and has a 6 for his STR score. This is our first time playing 5e together as a group, and none of us realized that in order to multiclass you need to meet the prereqs for both classes, not just the one you are multiclassing into.
He wants to multiclass into rogue, which makes great sense for his character, but is restricted from doing so because of his very low STR score and the requirements for multiclassing as a paladin. I offered to let him swap some of his abilities, but none of his other scores are much better and would still be pretty restrictive in terms of multiclassing. Swapping his DEX and STR would break his concept, since he's going for a swashbuckling pirate type character, not a STR-based heavy hitter.
Thematically it works out great for his character and I'm leaning towards letting him multiclass into rogue because his attacking ability is DEX (he's a finesse fighter), and he would meet the requirements if it required DEX instead of STR.
Best Answer
Problem?
In this particular case, nothing. Any concern you might have about "overpowered" is mitigated by his stats being at unimpressive levels. From your previous question you indicate that the players are not leaning toward min-max, power gaming, nor optimization in a munchkinny way. He's using finesse weapons that in time may limit highest damage potential: but if they aren't in min max mode, that does not seem to matter to the group.
At higher levels, he may get a little frustrated with melee damage since there are no two-handed finesse weapons and there are fewer choices in weapons ... but a lot of that gets into what fighting styles he uses and chooses. (And you control what magical weapons, if any, become available so you can tailor that to this party/team. Our DM did just that for our Bard, who is a rapier using singer).
At higher levels he'll benefit from those Divine Smite nova shots. When paired with sneak attacks from his rogue levels, he should be able to keep his damage in a "good enough" zone if the party fights well as a team.
The other place a low Strength would be a Paladin issue is in armor selection: if he wants Chain, Splint or Plate, he needs 13 / 15 / 15 strength respectively. With the proposed Dex build and Rogue multiclass, he's unlikely to want them since they give Disadvantage on Stealth checks. He can wear Breastplate with no minimum Strength requirement -- allows up to +2 of his Dex AC bonus, and no disadvantage for stealth. At 400 GP it may be a level or two before he can afford it. A 50 GP chain shirt may be his best for the time being.
From @Ethan's comment: With leather armor, a shield, and 20 Dex (After a ASI's) he will end up with 19 AC, 1 lower than full plate+shield, but the Piradin will be good at all +Dex skills. This makes for solid function when full plate isn't a good idea -- such as waterborne adventures. His damage output will be identical to a strength based shield using paladin (barring difference in MC class features).
If this is a role and story based move, all the more reason to go with it. It sounds like fun - which is why we play. As long as the player knows where the difficulties are up front with the stats as is, the player is taking on a challenge. Good on 'em!
I'd recommend a ruling to let him proceed as desired. (And if later on they finds some gauntlets of ogre strength ... )