Not fixed as far as I know. I recall riding eastbound on this section once and a couple ladies in the car remarked to me how rough the track was. I told them that we would be through it in a few minutes and the track would smooth out and of course it did. They thought I was a genius. I didn't try to convince them otherwise..
Living in suburban Springfield, MA I can attest to the fact that the Post Road cutoff was super rough as I'd be on 448/449 several times per year. Walking down the aisle or even keeping from sloshing a beverage all over oneself was impossible. Running at perhaps 50-60 mph only made it worse. It was super-choppy, far worse than the former CB&Q trackage in Iowa and Colorado 2 years ago. Somehow, Amtrak managed to 'fix' it perhaps 4-5 years ago. They still run at 50-60 mph, but the bumps aren't nearly as bad. Perhaps they used the same equipment that was used to replace the long gone 2nd track between Albany & Schenectady and install the 'missing track' at ALB after those projects were done. Give it another 5 years or so, it will be right back to 'full washboard' status again.
The CONO route is pretty rough. I thought sure I was going to be bounced out of the upper berth in our bedroom but wasn't.
I agree that the CONO route is incredibly bumpy, especially in Illinois. Riding CHI to NOL 3 years ago, between there being no baggage car or transdorm, the sleeper was directly behind the locomotive. The incessant horn kept me up most of the night, even after removing my hearing aids! And the rough ride made it seem like I was about to be thrown out of the lower bed in my roomette. But I DID end up with a number of bruises on my arms from banging side to side while sort-of asleep. Until that trip, I never had a 'DO NOT RIDE' route. The CONO made that list of one, hands down!
However...
I am presently in the New Haven station awaiting regional train #148 to take me back to Springfield after having ridden the Acela both ways NHV-WAS today. Opposite to what I experienced on former New Haven track NHV-NWO in a sleeper in April, all the trackwork they were doing back then has paid off! Other than running (I'd estimate) 50-60 mph, I thought the that track was surprisingly smooth! There's still a couple of slow orders here and there, though. PHL-WAS, the track was rough both ways. One of the attendants in First Class 'bounced' off the side of a seat south of BAL while bringing out meal trays northbound. New Carrollton to Baltimore was the worst!
As an aside...in the WAS Club Acela, trains were not announced on the PA. Regional trains were ignored. You were on your own to go through the main waiting area to your gate. For the Silver Star, an attendant talked loudly to get everyones' attention. About 20 minutes prior to departure of #2170, I asked at the front desk if they're going to announce 2170. After finishing with #91 passengers, the attendant called for #2170 passengers and directed us out the side door to the proper track, about a minute or two before the crowd from the main waiting area came out to the train.