It's seems to me that just putting a general warning about multiclassing being an "advanced option" Is all that's needed. If players choose to ignore the warning and find their multiclassed character is woefully underpowered then its on them, just as it is if they choose to ignore ability score recommendations when they create their character. There is only a limited amount of hand-holding that can be justified. Players have the right to make bad choices.
I tend to agree. I honestly don't think this is truly a thing done in the name of accessibility though. Learning that Larian is putting in a bunch of items specifically to make multiclassing easier and saying as much publically makes me think that they just WANT people to make absurd multiclass combos. It would fit in with their philsophy to date of stupid, crazy things being the most fun and encouraging those sorts of things (see for another example, all the items to buff spell attacks but the various nerfs to support and controll spells).
