After some digging I don't have a real answer but at least new informations to add to this conversation supported by some historical facts  .

Here is Peter Chubb https://www.youtube.com/watch?v=Sye3mu-EoTI in one of his speeches talking about the shell, around the 19:00 mark you can hear him mentioning why e is the alias for the default editor in unix shells, it's because older terminals where not so comfortable or easy to use and typing on them was an unpleasant experience  .

He is mentioning a precise model, the https://en.wikipedia.org/wiki/Teletype_Model_33 in this case  .

After some research ( http://www.pdp8.net/asr33/asr33.shtml ) I find that this machine only lets you pick in a pool of 64 characters, not even full US ASCII support  , 2 to the power of 6 chars, it's a 6 bit combination  .

Infact this machine has nothing to do with ASCII at all, meaning that it's not even supporting just the first 64 chars of an ASCII, it's just going for a totally unrelated set of inputs and probably not standard ( for our modern era  ) set of characters  .

The ASR 33 teletype can print 64 characters which only allowed for UPPER CASE LETTERS, numbers, and symbols.

from http://www.pdp8.net/asr33/asr33.shtml

and this just proves that it's definetly not US ASCII given the fact that to support uppercase letters you really need more than 6 bits, the uppercase letters are beyond the 64 chars mark ( or the value 63 in decimal if you want to follow a table  )

    0 NUL    16 DLE    32      48 0    64 @    80 P    96 `   112 p 
    1 SOH    17 DC1    33 !    49 1    65 A    81 Q    97 a   113 q 
    2 STX    18 DC2    34 "    50 2    66 B    82 R    98 b   114 r 
    3 ETX    19 DC3    35 #    51 3    67 C    83 S    99 c   115 s 
    4 EOT    20 DC4    36 $    52 4    68 D    84 T   100 d   116 t 
    5 ENQ    21 NAK    37 %    53 5    69 E    85 U   101 e   117 u 
    6 ACK    22 SYN    38 &    54 6    70 F    86 V   102 f   118 v 
    7 BEL    23 ETB    39 '    55 7    71 G    87 W   103 g   119 w 
    8 BS     24 CAN    40 (    56 8    72 H    88 X   104 h   120 x 
    9 HT     25 EM     41 )    57 9    73 I    89 Y   105 i   121 y 
   10 LF     26 SUB    42 *    58 :    74 J    90 Z   106 j   122 z 
   11 VT     27 ESC    43 +    59 ;    75 K    91 [   107 k   123 { 
   12 FF     28 FS     44 ,    60 <    76 L    92 \   108 l   124 | 
   13 CR     29 GS     45 -    61 =    77 M    93 ]   109 m   125 } 
   14 SO     30 RS     46 .    62 >    78 N    94 ^   110 n   126 ~ 
   15 SI     31 US     47 /    63 ?    79 O    95 _   111 o   127 DEL 

Thanks to this website http://keyboards.jargon-file.org/#ASR33 I can show you the input layout of such keyboard

There is also a bit more information about how the physical connections that generate the characters are coded http://jargon-file.org/jargon-html/html/B/bit-paired-keyboard.html ( the page also clarifies that ASR33 and ASCII chars are different down to the bit level  )  .

I think that it's interesting to note that there are no {or } but only ( and ) which means that probably creating subshells was ok but creating new processes was probably not so easy or permitted by the terminal  .

In the end I don't think that there is a real scientific answer, it was probably a "free" character waiting for a special meaning; one thing is shure tho: shells and terminals are older than ASCII and thinking about ASCII or any coded table as we know them today is probably not going to solve the mistery .

After some digging I don't have a real answer but at least new information to add to this conversation supported by some historical facts.

Here is Peter Chubb in one of his speeches talking about the shell, around the 19:00 mark you can hear him mentioning why e is the alias for the default editor in unix shells. It's because older terminals were not so comfortable or easy to use and typing on them was an unpleasant experience.

He mentions a precise model, the Teletype Model 33 in this case.

After some research I find that this machine only lets you pick in a pool of 64 characters, not even full US ASCII support, 2 to the power of 6 chars, it's a 6 bit combination.

In fact this machine has nothing to do with ASCII at all, meaning that it doesn't even support just the first 64 chars of ASCII, it's just going for a totally unrelated set of inputs and probably not standard (for our modern era) set of characters.

The ASR 33 teletype can print 64 characters which only allowed for UPPER CASE LETTERS, numbers, and symbols.^Source

and this just proves that it's definitely not US ASCII given the fact that to support uppercase letters you really need more than 6 bits, the uppercase letters are beyond the 64 chars mark (or the value 63 in decimal if you want to follow a table)

 0 NUL    16 DLE    32      48 0    64 @    80 P    96 `   112 p 
 1 SOH    17 DC1    33 !    49 1    65 A    81 Q    97 a   113 q 
 2 STX    18 DC2    34 "    50 2    66 B    82 R    98 b   114 r 
 3 ETX    19 DC3    35 #    51 3    67 C    83 S    99 c   115 s 
 4 EOT    20 DC4    36 $    52 4    68 D    84 T   100 d   116 t 
 5 ENQ    21 NAK    37 %    53 5    69 E    85 U   101 e   117 u 
 6 ACK    22 SYN    38 &    54 6    70 F    86 V   102 f   118 v 
 7 BEL    23 ETB    39 '    55 7    71 G    87 W   103 g   119 w 
 8 BS     24 CAN    40 (    56 8    72 H    88 X   104 h   120 x 
 9 HT     25 EM     41 )    57 9    73 I    89 Y   105 i   121 y 
10 LF     26 SUB    42 *    58 :    74 J    90 Z   106 j   122 z 
11 VT     27 ESC    43 +    59 ;    75 K    91 [   107 k   123 { 
12 FF     28 FS     44 ,    60 <    76 L    92 \   108 l   124 | 
13 CR     29 GS     45 -    61 =    77 M    93 ]   109 m   125 } 
14 SO     30 RS     46 .    62 >    78 N    94 ^   110 n   126 ~ 
15 SI     31 US     47 /    63 ?    79 O    95 _   111 o   127 DEL 

Thanks to this website I can show you the input layout of such keyboard

There is also a bit more information about how the physical connections that generate the characters are coded (the page also clarifies that ASR33 and ASCII chars are different down to the bit level).

I think it's interesting to note that there are no { or } but only ( and ) which means that probably creating subshells was OK but creating new processes was probably not so easy or permitted by the terminal.

In the end I don't think that there is a real scientific answer, it was probably a "free" character waiting for a special meaning; one thing is sure though: shells and terminals are older than ASCII and thinking about ASCII or any coded table as we know them today is probably not going to solve the mystery.