I got down there back in 2010
I vaguely recall the SR 27 signs in the early 80s. I wondered as a child why they just didn't route US 27 along SR 27 and then route US 27 as US 27E or US 27 Spur into Miami.
The main issues there would have been:
- FL 27 (current 997) was until very recently hugely substandard to any US Route in Florida.
- A child US Route would not make sense given the AASHTO has a long standing provision to not add sub-300 mile intrastate US Routes. If FL 50 can’t get an Intrastate US Route I suspect no other State Road stands a chance.
- Having an E/W split in US 27 would require it overlap US 1 from Miami to Florida City. In that case it would just be better to replace US 1 all the way to Key West with US 27. Although if the State picked up Card Sound Road again then moving the terminus to Key Largo might be more feasible (but would still require the Miami-Florida City multiplex of US 1).
Now what would be kind of neat (in a Fictional Sense) is having US 27 or another US Route end in Flamingo. Main Park Road is very solid for an NPS road and wouldn’t be without precedent in the National Park System. I think a realigned US 98 or 441 would make more sense than US 27 though.