[mmckenna]

Its a little slower, but generalizes the solution a bit.

func:{[td] c:where 0=type each flip td; / find which columns need unpacked 
           ocn:cols td; / store all original column names for order 
           ncn:`$raze{string[x],/:string 1+til count first each flip[y]x}[;td]each(),c; / calculate new column names 
           acn:ncn,ocn except c; / list of all final columns 
           c:raze {x where x like y}[acn;]each string[ocn],'"*"; / all final columns in order flip 
           c!flip raze each td / create final table with column names and column data } 
q)t 
a b 
---------- 
1 4 
5 6 
2 6 
12 23 
3 12 
36 14 

q)func t 
a b1 b2 b3 
---------- 
1 4 5 6 
2 6 12 23 
3 12 36 14 

q)t3 
a b c d 
------------------ 
1 4 5 6 
1 1 2 3 
2 6 12 23 
2 4 5 6 
3 12 36 14 
3 7 8 9 

q)func t3 
a b1 b2 b3 c d1 d2 d3 
--------------------- 
1 4 5 6 1 1 2 3 
2 6 12 23 2 4 5 6 
3 12 36 14 3 7 8 9