I should clarify after some study of 91.225 for gliders.

http://www.ecfr.gov/cgi-bin/text-idx..._1225&rgn=div8

TABS is always voluntary.

After 2020 a TSO-C166b 1090es ADS-B out (not just TABS or UAT) will be required

- In class A, above FL180. Presumably IFR without a wave-window.

Either 1090es or UAT (but not TABS) is acceptable

- Inside class B or class C airspace, or within that lateral boundary above 10,000' MSL (or the airspace ceiling, whichever is lower.)

Otherwise as with a transponder today, ADSB-out of any kind will not be required within the class B "veil" or generally in controlled airspace between 10,000' and 18,000' MSL.

Whew!