Two part post:
1) Signature Items for Legendaries
I'm against this because signature items honestly do not just magically become a fix-all for a Pokemon's issues unless we ridiculously overdo it. Primarily I'm talking about issues related to typing or movepool, since both of those tend to shaft most Pokemon. As Exclaimer brought up, Wormadam-S has an incredibly beefy signature item, but its still not that great because (a) Knock Off does exist and (b) Wormadam-S still has an incredibly limited movepool. A lot of these legendaries that 'need a buff' are the ones that have issues that really just aren't fixable.
Also worth noting is that very few Pokemon in ASB are just downright unusable (I'm looking at you Parasect). It's up to the Pokemon's user to make it work. I mean, we all joke about Primeape just not being good enough in our metagame, yet Matezoide consistently uses his, and performs very well with it, even having it duel a Mega Gardevoir to some extent. A lot of what makes a Pokemon 'bad' can often be circumvented if you know what you are doing with them, and Legendary Pokemon are just another facet of this. Example, if Ho-oh's 4x weakness to rock is really a problem, just run Focus Band or spam Sacred Fire until a burn is rolled. Either option gives it a lot of defensive help so that it can just do Ho-oh things and spit out damage.
2) A Potentially Horrible Suggestion
Alright, so messing around in IRC last night, the discussion of adjusting the rank 3 floor came up once more. More specifically, sending it down to 60 instead of 61, as to include a lot of Pokemon that got stuck with rank 2 in certain stats where a 3 may be better for it. But after thinking on it some more, I really want to suggest this change as at least a discussion point to hear arguments for an against it because Generation VII did not really bring much change to our metagame, and I think this slight change could bring quite a few Pokemon out of the 'almost good enough' category.
My Perspective
- Buffs some Pokemon that otherwise wouldn't see the light of day. Example: Zoroark goes from 90/4/2/5/2/105 to 100/4/3/5/3/105, one bad set of bulk to one good bulk set.
- Buffs some Pokemon that probably really just don't need the buff. Example: Kecleon goes from 90/3/3/2/5/40 to 100/3/3/3/5/40, but it was already heralded as good prior to this.
- Some of these changes actually hurt the affected Pokemon more than it helps them. Example: Cherrim gets an extra rank in Atk, but that causes it to lose the +2 SpA it got from Rare Candy
- Despite the vast variance in effects this change could have, I think it's worth at least considering just as a jolt of viability to ASB, since otherwise we'll just keep being stuck in the same stale metagame.
For those who want/need it. I've compiled a list of what Pokemon have what stat boosted
here.
EDIT @ Below: For Spinda, that's just not true. Spinda's change actually has the exact same stat yield as before, just much less dependent on the Everstone (see: Knock Off only removes 1 rank of stuff instead of 2).
Also, not sure how going 4/2/2/3/95 to 4/3/3/3/95 is suddenly unplayable. You might just need to change natures to Adamant or run RageCandyBar or something.