I'm basically not going to say no to adding new content, but I'm really, really opposed to anything being balanced around max iLevel+bleeding edge players. I mean, we're talking groups who took out A3S after a week, with Ravana weapons, and then scaling difficulty up to account for another 20 ilevels. It'd be a much more demanding fight than anything we've seen. That level of difficulty is straight up insane and would render the trial useless for all but probably less than 50 groups worldwide until the next tier. Plus gear walls just aren't fun. A4S is balanced pretty heavily around assuming a certain level of player HP; less than that and you're in for a really bad time (especially if for some crazy reason you're doing Nisi), more than that and eventually a lot of the mechanics aren't going to matter as much.
I do think there should be something in the odd-numbered patches for the 'hardcore' group in general. I like the idea they had with Savage SCoB -- reuse old content, have it play differently, have it be challenging--and am pretty disappointed we never got Savage FCoB. Them revisiting old content and releasing new, scary iterations on odd-numbered patches would be ideal, really. Chop up CT and release CT Savage, come up with yet another way to make Titan crazy and release that, Shiva has basically needed a Savage version since introduction, etc.
I'd just tune it a little lower than you're aiming. World first groups by their nature are going to blow things up quickly; that's their goal and they go hard for it, and I think they kind of expect that. The really super hardcore groups are pretty good at finding ways to introduce challenge into fights without them being tuned to be impossible at anything less than max gearing. Leave it tuned low enough that other people can aspire to it, too.
We've seen that titles alone won't do it, but I think a lot of that just falls back on 'is it fun' and 'are we bored enough to do this yet?' I think if it were a regular thing--raid groups could expect even numbered patches would have progression raids and odd numbers would have challenge bonus raids--people would take to it eventually regardless. Savage SCoB as a one-off that essentially only rewarded bragging rights was a freak event.