I think people are getting way too caught up in the "work with CC not in spite of CC" idea. I think we need to take a step back and realize that CC is a shit ability. Compromises are going to have to be made somewhere; if not in its role, its typing, stats or movepool. Give it a really strong defensive initial typing, and you don't bank on CC much because you would rather be your initial typing - you could argue we'd be working around CC rather than with it here. Make it too weak, and 29 isn't switching in on anything. This is similar for stats and movepool stages.
Of course we would rather make a mon that works with CC. That's a given, and no sane person would argue with that. How idealistic are we being about it though? How high is the bar for "interacting with the ability?"
A couple people have argued that a pivot wouldn't interact with CC. I'd disagree. The Keckleon v Wailord example is perfect. Keckleon comes in, resists Water Spout, recovers or uses a utility move, then switches out when the opponent brings the next mon in. There is no way Keckleon would be able to do that without CC. How is that not a perfect example of a pivot interacting with CC?
To kjn's points: the interaction is absolutely about the typing we change to. Sure, a good typing on switch-in is important, but so is the 80%-1 to 20% damage interaction. What 29 could do that other pivots can't is switch in on neutral or SE moves, and resist them the next turn. Granted, we probably aren't switching in on CB Rillaboom Wood Hammer if we're a base Water type, but not many mons can do that. Quziel offered a nice example on Discord of thinking about a CC Metagross vs Astrolotl. We are able to come in on an SE hit, laugh off a potential second hit, threaten out the opponent, and gain free turns as a result. This is absolutely a function of the type we turn into, rather than the initial typing. Plus, I'd argue that other defensive mons can't function like this. Additionally, you could also argue that other defensive mons can use bulk up and/or wallbreak.
What will set 29 apart from other mons is this: 29 should be able to use its ability to generate those 80-20 situations to live hits. We need to give it the tools to do this, as well as to force opposing mons out, be it through threatening a powerful hit, status, knock, spikes, set-up, etc. Because of its ability to force other mons out, we will generate free turns.
Now do we want to use those free turns to steal momentum, use utility options, set up for a sweep, or use a high-powered move off a high attacking stat to punch holes in the opposing team? Each of these has its merits and demerits. But I think it's strange to argue that any one of these is "not interacting with the ability," because these situations are only created by virtue of CC.
Now here's my take on set-up:
A set-up mon is in a unique position to make even chained SE hits less threatening by boosting defenses. But it would still be suspect to the usual pitfalls of defensive set-up: revenge-killing, phazing, and toxic. Think about the defensive set-up mons that are successful in the meta. It's basically Clef and Magearna, maybe Fini? These are all immune to toxic, and have spammable stabs. Magearna has shift gear, a strong stab, a snowballing ability, insane defenses and defensive typing, and high sp. atk. I doubt we're going to give 29 all those toys unless we're making a 600 BST mon. Clef and Fini are still able to do stuff when not actively setting up.
So we'd be setting out to make a Clef or Fini that isn't immune to toxic and probably won't have STAB most of the time? We could definitely do that, but we would need to compensate heavily in the later stages in order to make it work. Being a newbie to this process, I am kind of worried that we will become pre-occupied with giving 29 enough strong stuff to function as a set-up mon, rather than focusing on CC as the concept. I also don't know if beefing up the stats, typing and movepool would count as "working in spite of CC rather than with it."
I am not currently convinced by any of the roles I have mentioned, and am not leaning in any particular direction at the moment. Also, I've only focused on BU and CM as set-up options here. There's also Cosmic Power, but I feel like that's a different can of worms.