one current approach for insertion.
z=.1 0 1 #^:_1 'ab'
]z=.'a' (1)}z
'aab'
shorter:
'a' (1)} (1 0 1 #^:_1 'ab') --- 'aab'
for more direct gap insertion with }..
'a' (1)}.. 'ab' --- 'aab'
with }.. or..... some other glyph.
(9) 1}..1 2 3 4 5 --- 1 9 2 3 4 5
(9) 0}..1 2 3 4 5 --- 9 1 2 3 1 4 5
(9) 5}.. 1 2 3 4 5 --- 1 2 3 4 5 9
(9 10 11) 2}..1 2 3 4 5 --- 1 2 9 10 11 3 4 5
(9 10 11) 2 3 }..1 2 3 4 5 --- 1 2 9 10 11 3 9 10 11 4 5
(9) 1}.."1 ( i. 2 2) ---
0 9 1
2 9 3
(9) (1+#z)}.."1 ( z=.i. 2 2) ---
0 1 9
2 3 9
Uiua uses glyph completion (Mnemonic glyph completion from ASCII sequences) and that enables new glyphs. No need for a new keyboard or labels. Perhaps '⋔' for gap insertion. Maybe direct gap insertion allows in-place.