CapnZapp
Legend
Isn't this overthinking it?@tetrasodium
Am I understanding you right? You are saying, there can be a magic item, whose benefit is to grant the ability to attune a number of more magic items. So, for a DM who wants to run a "christmas tree" campaign, there is an easy way to do this, by introducing this "attuner" magic item into the campaign. Not a bad idea, and is an easy way to offer a "modular" option for this old school play style. Probably this magic item should be separate from the treasure list, and in a section dedicated to a many-items style of play with advice on how to balance and manage it.
Why can't the DM wanting a more 3E-style christmas-y campaign just double, triple or outright remove the attunement slot limit? Without asking for permission from the DMG first I mean.
Making an object out of it is probably bad, since, even if the item is explicitly labeled optional (like all items aren't optional already), it will give the impression the game somehow needs a bigger attunement slot limit.
(Maybe I'm misunderstanding and you can ignore this post)