I will add to my horror of this possible change to Quivering Palm. The old base against the boosted DDO saves made it utterly useless. I understand that adding a boost on fails would make it eventually useful, but having to expend 30 Ki on a move that is useless for the first 5-10 clicks is just inane. I for one wouldn't waste my time and Ki - I'd just go with an elemental move that actually does something.
So obviously the concern here is how to bring it to something that you CAN build for, but make it where you actually have to take effort to reach reliable QPs.
One option is to have it as just a "combat" skill with no sundering - that automatically shaves off 10-12 DC. You can still get it into the 60 to 70 range with max investment, but it takes effort rather than the light investment it does now.
Another option (as suggested by Andoris), is to give more ways to boost Monk moves in general, as Quivering Palm was far from the only move that was useless outside of low level quests. ToD, Dismissing, Jade, etc are all moves that face low DCs as they have nothing to boost them. Putting QP at full level and making things like Henshin Mystic training apply to all monk moves instead of just finishers as well as having Grandmaster of Flowers apply to it all could be a nice overall fix. My only issue with this solution is it loses a bit of the "work" type investment with things like PLs into Fighter. It also forces being in GMoF for effective DCs as you can't twist and stat invest in other trees.
Then there is the third option - increase the timer and/or Ki cost. Also possibly bring it back to unarmed only.
That said, I also do think QP SHOULD be more successful considering it already has weak points.
Quivering Palm can only hit one target, costs Ki, requires you to be in melee range, requires you to successfully hit. It has a short cooldown, but you're stymied against groups of targets. If you can just face tank it, then you can slowly QP them through. If not, kiting could work for a bit, but you won't have the Ki to quickly dispatch them. Doesn't work on orange names+.
Assassinate has no cost, but you must be in stealth, easily hits two targets as it triggers on both the forward and back action of your swing and can hit more with double/offhand strikes, does 10d6 bonus damage on a save. Works on orange names, but not red names+ (though you still get the bonus 10d6, so worth first hitting from stealth). It doesn't reveal you from stealth, so you can slowly assassinate through everything assuming you have high enough sneak. Stealth has been greatly improved in the U19 pass, so even if you do get discovered, you can escape notice and continue on.
Death spells are ranged (other than Slay Living), Wail is PbAoE and works on even untouchable targets (suck it earth elems), cost SP. They also have rather long cooldowns, but with multiple death options, handling large groups is easy assuming you have your DCs in place. Anything your Wail doesn't kill, you just finish off with Fingers and Power Words. There's a reason they're "god mode" once they reach no fail DCs. SP is a "limiting" factor, but with so many clickies and regen options, lasting between shrines is not difficult. Of course there are always SP pots for infinite SP if you are so inclined.
Wiz/Sorc should have the most difficulty reaching DCs due to their multitude of insta-kill options that include AOE kills. Assassinate does indeed need a little love on their DC options - more items (instead of only two, one an Iconic only and the other an old Epic) including ones that reach +5. Also the possibility of Rogue past lives adding +1 would be welcome. Quivering Palm Monks is actually the weaker kill option, but as it's easily reached, anyone can do it, and thus everyone does. So the key term is to either take it out of easy reach, or make it have a heavier price... however the u21 proposed solution is not the right one.