Austrobogulator: It's definitely harder than just vertical lines/diagonal lines, but easier than the enigma code :o
MadalinStroe: I tried all 16 rows and their 15 rotated permutations = 256 permutations
I tried all 16 columns and their 15 rotated permutations = 256 permutations
I tried both diagonals and their 15 rotated permutations = 32 permutations
After 544 tries I give up until a clue is released.
I'm expecting something more elegant from Austro.
For example, there are a few pairs of letters that occur more than once:
(This includes pairs that wrap to the next line, but it's just an example.)
3m, uc, 5a, j5, mj, rj, bh, it, ni, 7m, v7, e9, cc, h8, 9v
There are 15. Stitched end to end with overlap, this could form a 16-character code.
e.g., 9v + v7 + 7m + mj + j5 + 5a = 9v7mj5a etc.
This particular avenue doesn't work, but it's an example of something less arbitrary than performing one of 544 equally valid rotations. I'm certainly not criticizing you, though. I'm happy you ruled it out!
If you at the rows and columns, you'll find more repetition in columns than in rows. ( Below will be much clearer if you cut and paste it into an editor with a monospaced font. Also, the lines were sorted via script, but I picked out the multiples by hand, so they may contain errors.) Do with this what you will.
vertical:
12357ACDHKLOPPTZ PP
3336777DDEEELLMM 333 777 DD EEE LL MM
036GHIMMNNNQQSTY MM NNN QQ
2235FIJKMMMRRTVY 22 MMM RR
33448AAANNNTTUUU 33 44 AAA NNN TT UUU
0256BCDFJKQQRUVZ QQ
447HJLLOOUWYZZZZ 44 LL OO ZZZZ
036AGIJJKMNQRUVZ JJ
1489BBHKKKKMVWYY BB KKKK
116668EEEJJJUUYY 11 666 EEE JJJ UU YY
5558999AACCCLLMM 555 999 AA CCC LL MM
1145ACCDHNOSTVVV 11 CC VVV
37ADEEIILOSVVVXY EE II VVV
115777HHHIIRRRXX 11 777 HHH II RRR XX
113888JJJMMNNTTT 11 888 JJJ MM NN TTT
2345BDHIKLNOPRRS RR
horizontal:
367BDGLLMOQTUVYZ LL
2458DEFIJNTTTXYY TTT YY
134789AEHIILNQSV II
5689BCCEHJKLNQRR CC RR
01456AAADEEKNNRU AAA EE NN
1237778ABHJJMNOV 777 JJ
111236BCEMTTVYYY 111 TT YYY
2455DFHJJKQRTUUV 55 JJ UU
3447AAJKMNPQRSYZ 44 AA
0139EHIJJKKLMOTX JJ KK
133555IKKLMMNSUW 33 555 KK MM
334888DDDHHILNOZ 33 888 DDD HH
02667CEHHJMNRRSW 66 HH RR
36ACCKLMMNOUVXYZ CC MM
79AGILMORRTUVVZZ RR VV ZZ
11357CIJMMPPUVVZ 11 MM PP VV