If their intent was to get rid of BL 80, then they should sign the eastern half as CA 51 and call it a day.
I don't think they were trying to get rid of Biz 80, but simplify signing since locals tended to refer to that section as US 50 only.
As mentioned in the other thread, the state's highway law stipulates that SR 51 shall be signed as BL 80, but the US 50 portion of the business route didn't have that distinction.
I am still waiting for someone in the Sacramento area to request lawmakers remove that law to eliminate Business 80 in full and allow SR 51 to be signed as SR 51 or perhaps as SR 99. (Yes I know that moves SR 99 traffic away from its implied overlap with US 50 and I-5 and away from its continuation north of the airport, but it seems logical given SR 99 is the through route when traveling through the US 50 interchange heading northbound.) Joe Rouse might be able to tell us if someone is pursuing that goal, since it seems silly to have Business 80 take a spur southwest to the US 50 interchange and end without an apparent reconnection to its parent. If you're going to get rid of the route, might as well get rid of the whole thing, not just the US 50 section.
For what it is worth, California in general has deemphasized business routes of any type. Local municipalities typically do a poor job of maintaining signage for business routes, and there is no state law requiring municipalities or counties to sign their business routes. So unless the business route happens to overlap a state highway, the business route is more than likely unsigned. But with that said, Caltrans hasn't really enacted many new business routes (I can think of one on SR 58 at Mojave and another on SR 4) in the past ten years. Very few business routes remain in Southern California (I-10's loops for places like Indio and Colton are largely unsigned and therefore decommissioned, except for a couple of remnant shields), and I think they are getting less and less frequently found on rural freeways such as US 101 (Paso Robles), I-80 (Truckee), and I-5 (Redding). I am sure others on the board can cite additional examples.
In general Caltrans seems to be interested in removing Business Routes when possible. When the CA 43 roundabout was completed last year the Business Route 198 signage was removed entirely. Most of the Business Routes I encounter are just a single guide sign or shield which likely was part of a higher degree of signing.
I see this trend as a function of the use of GPS and onliine mapping services available while driving. In the past, if you wanted gas, food, lodging they were found right on the highways. As individual bypasses were built, people who wanted to partake of those services could generally find them along the old highway corridor. And for many small cities, you can get directly to the old highway corridor by taking the first exit of the town, follow the old highway through town and be deposited right back onto the freeway at the other end. It was important for people to know that they could simply keep driving in the same direction to get back on the road, as opposed to doubling back and heading back to find an on-ramp where you exited (in some cases the ramps to business routes are unidirectional and don't serve the minor direction).
But now, your online service can tell you where the services are and how to get back to the freeway. So the need for such signage has diminished greatly.
I, like many of you road enthusiasts, enjoy driving business routes to get a feel for a town that I may be passing through. Take an extra 10 minutes to see what there is. Try to imagine what it is like to drive this road back in the 1920's and 1930's when this was the main road. But it is harder now that the signage is gone and outside of certain historical examples like US 66, the municipalities don't really seem to care.
That being said, I don't have any nostalgia when I drove Biz-80 in the late '90s when I lived in Northern California. It was a freeway and its purpose was to get to my destination as quickly as possible. If I wanted nostalgia, I would drive the true business route through Sacramento along West Capitol - 16th- Del Paso -etc.
Oddly enough, I would have less of a philosophical problem if the Tower Bridge Gateway (back in the '90s this was a freeway connector between the bridge and I-80, now its largely a surface route) and CA-160 freeways [and the surface streets in Downtown Sacramento between them] were signed as Biz-80 as this followed the old US 40 corridor and actually led to some businesses. And it provided a decent way to get a feel of Sacramento and then guide me back to I-80 to continue my journeys.