I think the SF control serves the purpose of telling people the way to get back to I-80. Likewise, for the other direction, the Reno control serves the same purpose so there is really no need for the Biz-80 designation. Let's get the legislation passed.
What is interesting about the sign is that D3 removed designations while D7 added designations. As many know, this sign used to read Biz-80 west to I-5, so the sign used to have 3 designations (50west, Biz-80 east and I-5) and now only has US 50. (IMO this is much better, US 50 alone is much simpler.) In constrast, in Downtown LA, signs along the southern section of the 101 used to read "5 Santa Ana/ 10 San Bernardino" now read "101 south to 5 south 10 east 60 east". More designations of highways but no control cities at all! (I would prefer a sign that says US 101 south Santa Ana/San Bernardino and supplemental signage on the shoulder saying traffic for 10 east, 60 east and 5 south should follow 101 south.)
The Catrans districts indeed operate like separate fiefdoms.
Seeing as how current SoCal idiom tends to emphasize the route number as the sole reference to a particular freeway, the "TO" multi-route reference probably isn't terribly inappropriate down there. D7 seems to go through alternating phases of "simple" vs. "comprehensive"; the more recent signage seems to indicate a bias toward the latter under the current district regime. That being said, I would think that a little of that thinking might benefit the D3 signage game, particularly in reference to the Oak Park 50/51/99 interchange; my choice would be to append "To West I-80" on the SB 51/Biz 80 approach -- but only if 51 still carries the Biz 80 signage! If, on the other hand, if actual CA 51 signage eventually supplants the green Interstate shields, then the business loop concept will have effectively dissipated and directions to get back on I-80 likely would be unnecessary. And, IMO, signage onto 51 should read -- from all Oak Park approaches "CA 51 to east I-80/Reno", and from WB I-80 "CA 51 to south CA 99". Period. No US 50 reference needed, as the major portion of that route involves something of a backwards angle from the generally SW trajectory of I-80 in the region.
Finding a good control city for NB CASR-51 isn't easy. Perhaps "Midtown Sacramento" or "N E Sacramento" or "Arden / Arcade" would work. Whatever you signed at Oak Park could be used SB at CASR-244 and then sign "Fresno" once you pass about H street. (or even the American River). Another idea is "American River Bridge" or whatever the bridge is eventual called ("John Sutter" or "Florence Truton Clunie" or "William Bancroft" or "Lynnette 'Squeaky' Fromme" Bridge). There is precedent for this in the Bay Area: "Golden Gate Bridge" and "Dumbarton Bridge". How is EB CASR-92 signed at US-101?
I don't see a need to change the control cities on 51. Just because the number that is signed has changed doesn't mean that the road goes to different places. The control for NB 51 is now Reno and should remain Reno as its main function is to lead to I-80 east from the eastern side of Sacramento. (There are many examples of this in CA where the control for a road is beyond where the road goes, but rather to a destination that the road leads to. And this is OK. Example I-680 NB to Sacramento doesn't actually go to Sac but leads to I-80 which does.)
For SB CA 51, the control between I-80 and CA 160 is rightfully Sacramento as it takes people towards downtown Sacramento. (I would also add the control Fresno because at this point it is an important connection towards CA 99.) At the CA 160 split, the signage has an interesting history. In its earliest days, this was the split of US 40 to 12th St Sac and US 99E to 29th St Sac.
See:
http://archive.li/VyU0uIn the early interstate era, this road was I-80. I imagine this had a control of SF, but I don't know for sure if that was signed at the split.
In more recent times, the sign has said "Biz 80 Capital City Fwy to US 50 and CA 99" and now says "Biz 80 Capital City Fwy". I believe that this should be streamlined to read "CA 51 south Fresno San Francisco" (without the need for reference to other freeways.)
(The on-ramps to the freeway at both Arden and Expo currently have a control of SF. If feasible, Fresno should be added to these signs if the road is signed as CA-51.)
FWIW, I'm glad that they signed the WX as US 50 instead of Biz-80 or (gasp) I-305. It makes no sense to change the designation of the main e-w freeway in Sacramento. And if you think that signing it as I-305 is too crazy, how do you explain signing the western section of CA 24 as I-980. IMO, its an unnecessary and confusing designation.