Whenever I hear of a Congressional proposal that is touted as saving us some billions or trillions OVER A DECADE, I know that 1) it is worded that way in order to sound impressive and 2) it will never come to pass because events still to happen will intervene.
For example, by 2028, the USA will be providing free medical care to the inhabitants of the whole world, so that will offset all of the Pelosi promises. Seriously, all sorts of giveaways are already promised by almost every Democratic contender for the presidency, and all of them would totally offset this Medicare change.
Incidentally also, when the Trump tax reform bill was passed a couple of years ago, some of its provisions were to kick in only after a few years (many fewer than Pelosi's proposal) and Democrats immediately said that before this could happen they would repeal it--which of course is possible.