Speaking of old BASIC interpreters, does anyone know out why DECSYSTEM 20’s BASIC had a “LISTREVERSE” command? 

Yes, it actually did exactly what it sounds like! 

Chalk one up for DEC and BASIC. What other programming languages support that feature, huh? 

https://imgur.com/a/Bt40M

DECSYSTEM 20 BASIC User's Guide: LISTREVERSE command

LISTREVERSE
LISTNHREVERSE

LISTREVERSE and LISTNHREVERSE print the contents of the user's memory area in order of descending line numbers. LISTREVERSE precedes the output with a heading, LISTNHREVERSE eliminates the heading.

LISTREVERSE

EQUIV                              10:53                                       13-NOV-75

40    END
35    PRINT "THE EQUIVALENT CURRENT IS",I, " AMPERES"
25    I=E1/R
10    INPUT R
5     INPUT E1

READY