Can an appropriately-fitted UAS (of any size category) be flown in Class B airspace?
In general, no, you can't.



Public (Governmental) Use

The FAA maintains a page on Public Operations of UASs. There are a couple of ways governmental organizations (excluding the armed forces) can fly a UAS:


It can fly in accordance with the limitations set out in Public Law 112-95 Title I, Subtitle B, Section 334 (c)(2)(C), which are that the FAA will:



  (C) allow a government public safety agency to operate unmanned aircraft weighing 4.4 pounds or less, if operated—  
  
  
    (i) within the line of sight of the operator;
    (ii) less than 400 feet above the ground;
    (iii) during daylight conditions;
    (iv) within Class G airspace; and
    (v) outside of 5 statute miles from any airport,
    heliport, seaplane base, spaceport, or other location
    with aviation activities.
  


So, obviously, that's a no-go for Bravo.


It can apply for a Certificate of Waiver or Authorization from the FAA, which "permits public agencies and organizations to operate a particular aircraft, for a particular purpose, in a particular area." According to the FAA,



  The FAA works with these organizations to develop conditions and limitations for UAS operations to ensure they do not jeopardize the safety of other aviation operations. The objective is to issue a COA with parameters that ensure a level of safety equivalent to manned aircraft. Usually, this entails making sure that the UAS does not operate in a populated area and that the aircraft is observed, either by someone in a manned aircraft or someone on the ground to ensure separation from other aircraft in accordance with right-of-way rules. Common public uses today include law enforcement, firefighting, border patrol, disaster relief, search and rescue, military training, and other government operational missions.


So, unless you have a really convincing argument, it sounds like the FAA is very unlikely to include in your COA authorization for your UAS to enter Class B (or get anywhere near it, for that matter.)



Civil, Non-Hobbyist Operation

The FAA also maintains a page on Civil Operations of UASs. That page summarizes how civil UAS operations can be approved as follows:


  There are presently two methods of gaining FAA authorization to fly civil (non-governmental) UAS:  
  
  
  Section 333 Exemption – a grant of exemption in accordance with Section 333 AND a civil Certificate of Waiver or Authorization (COA); this process may be used to perform commercial operations in low-risk, controlled environments. Instructions for filing a petition for exemption are available here.  
  


Surely, operating in Class B isn't "low risk" (though I suppose you could argue it's "controlled,") so this certainly seems like a no-go.


  
  Special Airworthiness Certificate (SAC) – applicants must be able to describe how their system is designed, constructed, and manufactured, including engineering processes, software development and control, configuration management, and quality assurance procedures used, along with how and where they intend to fly.  
  
  
  
    a. SAC in the experimental category – may be used for civil aircraft to perform research and development, crew training, and market surveys; however, carrying persons or property for compensation or hire is prohibited. FAA Order 8130.34 is used by FAA inspectors to issue experimental airworthiness certificates and special flight permits to UAS. For more information, please contact the Airworthiness Certification Service, AIR-113, at 202-267-1575.  
    
    If the FAA determines the project does not present an unreasonable safety risk, the local FAA Manufacturing Inspection District Office will issue a Special Airworthiness Certificate in the Experimental Category with operating limitations applicable to the particular UAS.
    
    b. A UAS type and airworthiness certificate in the Restricted Category (14 CFR § 21.25(a)(2) and § 21.185) for a special purpose or a type certificate for production of the UAS under 14 CFR § 21.25(a)(1) or § 21.17. For more information, please contact the Los Angeles Aircraft Certification Office at 562-627-5200.
  


(Bold emphasis is mine, italics emphasis is from the FAA.)

For UASs with a Special Airworthiness Certificate, FAA Order 8130.34C specifies in Chapter 3, Section 1.3 (Flight Test and Operating Area) that:


  All proposed flight test and operating areas outside of restricted airspace must be approved by the FAA. Flight test and operating areas will be coordinated with the air traffic component of AFS-80.


and that:


  The flight test area and operating area must be over open water, or sparsely populated areas, having light air traffic. The FAA is required to evaluate each application to determine that the proposed flight area does not exceed that which is reasonably required to accomplish the program.


Certainly, Class B doesn't qualify as "sparsely populated areas, having light air traffic," so this, too, seems to be a no-go.