Thirds is definately possible - major 3rds.... I wish I had my notes in front of me, as I'd give you the exact string gauges required, the names of the strings, and the tension.
Interestingly enough, I made the mistake of mentioning 3rds on Sticklist... and that sent off all kinds of warning flags....
Trust me - 3rds - Major 3rds as far as my 12 string TT Mobius Megatar Toneweaver goes - is a very very exciting tuning 😉 😉 😉
Big George W
East Derby CT
Mobius Megatar - tuned in Classic Stick Tuning [5ths/4ths]
M.Megatar Toneweaver - tuned in Major 3rds
Warr Phalanx 12 - tuned in 5ths [melody], 4ths [bass]
digitech, T.C. Electronics, ART, Lexicon, GK, Markbass, EA, Bag End, Guild/Hartke, SWR, EV, Radial, Ampeg, Trace Elliot, Furman