Does the FAA construe FAR 91.225 to prohibit aircraft w/o electrical systems w/o ADS-B-out from flying above 10,000' MSL unless below 2500' AGL?
The content in this FAA link indicates that the answer to the question is "no".


  Under the rule, ADS-B Out performance will be required to operate in:
  
  
  Class A, B, and C airspace. 
  Class E airspace within the 48 contiguous states and the District of Columbia at and above 10,000 feet MSL, excluding the airspace at
  and below 2,500 feet above the surface. 
  Class E airspace at and above 3,000 feet MSL over the Gulf of Mexico from the coastline of the United States out to 12 nautical
  miles. 
  Around those airports identified in 14 CFR part 91, Appendix D. 
  
  
  The ADS-B Out rule does not apply in the airspace defined in items 2
  and 4 above for any aircraft not originally certificated with an
  electrical system or that has not subsequently been certified with
  such a system installed, including balloons and gliders. For
  additional requirements for using the exception for item 4, please
  refer to CFR 91.225 section (d) for the requirements.


(italicization added)

(as of Feb 24 2020, the quoted web page had last been updated on August 22, 2019)