Amtrak recently refurbished *or are still in the process of* refurbishing the Superliners to keep them going until they can order the SL-3's, so you will be riding the current equipment for a few more years at least.
I know Amtrak did a big project prior to the current president where most of the Superliner-I's were redone, so sleepers got new bathrooms, upgraded wall treatments, and new carpets/drapes/cushions. But I'm not aware of this being an ongoing project. I've ridden in some of the S-II, where the flooring in the lower entrance is original and badly worn/buckled, and the bathrooms are all original. The S-II's are the most prone to toilet malfunctions at altitude on Raton Pass. If anyone knows specifics on a ongoing rebuild project, would love to hear about it, but other than the few TIGER rebuilds of bad wreck damaged cars, I don't know of any other rebuilds in recent time other than normal maintenance. But I'd love to be wrong.