I'm a Juggernaut-Main too. Forgive me if I make the wrong assumption, having seen many of your comments on the boards regarding Juggernaut champions, I assumed you were one as well. So here's my two bits on your post.
You bring up good points, but this part you said here...
[{quoted}](name=Big Lincoln,realm=NA,application-id=3ErqAdtq,discussion-id=ZMuEZ6Ih,comment-id=,timestamp=2017-04-10T23:38:13.509+0000)
items that would conditionally provide them what they lack in their kits (initiation, anti-disengage)
It kind of goes against what Juggernauts are supposed to be. In the post made by Riot with the Juggernaut Update, it said...
"Juggernauts. When you think brute force, these champions should come to mind: powerful, durable, immobile and melee."
Now pay attention to one particular word. "Immobile".
That means they're supposed to slow to get around, or if you want the literal sense of the word, not move AT ALL. (Of Course, on the latter that's not really the case and thank goodness for that.)
So, they're not meant to have initiation-type abilities or items because it goes against what they are designed to be.
On the subject of anti-disengage, many (Not all at this point in time that are considered Juggernauts) have anti-disengage built into their Kits.
For Example:
Has his E
Has the dash from her W
Has his W-Wall to prevent escaping provided he places it right
Has the speed boost from his Q (Might not be the best example considering Garen's current state but it nonetheless exists)
Now, granted, these abilities may not always WORK as anti-disengage due to the kits of some of the more mobile champs these characters may face. It's even HARDER for the ones that are Juggernauts according to Riot's sub-class list that have NOT gotten any form of gameplay change to GIVE them anti-disengage.
https://boards.na.leagueoflegends.com/en/c/developer-corner/3A5uuBw7-champion-subclass-list
So, in MY mind at least, I think there MAY be another "Juggernaut Update" in the future (Can't say when, can't say HOW it will be, I don't work at Riot) that
might introduce more diverse items that may fall in line with the suggestions you put forth here.
All in All, good post.
http://imgur.com/t/upvote_gif/v7RaQLO