I think your debuff [option 1] idea could work for a particular dungeon or something that has fitting with debuffs/diseases and such, but I think players might get annoyed at trying to do any dungeon content and then unable to successful do content in general afterwards because of it. Thus secluding it to a singular event should probably work for a way of increasing drop rates at greater risk (as well as really making the dungeon unique if it was fitting like I said "diseases" or something).
The second option is like a difficulty slider, thats always been an effective tool

. I just hope that the devs will consider AI patterns and not just do flat rate buffs like hp + X %.
One of my suggestions:
RNG over a large data set = amount of attempts SE would like a player to take before getting the reward.
I.E. 50% drop, expect players to try twice (its a bit generalized math but close enough).
Instead of using RNG for certain drops it can easily be turned into a token system, something SE has already had planned [100% token drop rate on failure to loot rare item]. Unfortunately the awesome drops are not turned into a token system, you can only buy lesser drops with the tokens.
I think one of the reasons they didnt do a token system for the harder drops is because often when the rates are converted to a fixed number you will find they had planned for some people to do it many hundreds of times (and you just got lucky). So they dont want you to realize how "big" the grind actually is. That and there is a psychological effect to chances that some people find addicting.
Its why I like promoting the progressive percentage system. Pick a general % you want. Now pick lower then that and start players on it, as they fail the run increase the % at a growing rate until they succeed, restart %. Never will your run be useless even if you didn't get anything, you will always be more likely to win than the last time.
You can make the reward a token that can be switched out for a particular item. So rather then 100 tokens = item, re-denominate for the fact tokens are now rare. (You can just use 100% tokens on rare items and ignore a chance system but like I said players might be disheartened to see some gear costs 500 runs - to hide that you can use the progressive %'s I suggested which rewards effort but is still a bit on chance as well).