Bitcoin script is pretty small as each codes only have 4 byte in size, so it only save less than 16 bytes and contribute little to reduce blockchain size growth.
Also, all wallet must adopt to this format and i doubt it can be done without hard-fork, unless you introduce new opcodes and older nodes treat it as anyone-can-spend (just like SegWit backward compatibility). Roughly it look like this where nodes automatically convert it to proper script and put the signature to correct position.
OP_PRESET
Using this method means that you can get size of input signatures down from O(n) to O(1). There is also space saving on the outputs because you only need to use a pub key and not other scripting stuff.
It's still has O(n) space complexity unless you're talking about MuSig Schnorr
I mean with this technique you can introduce signature aggregation (only need 1 signature for N keys). So it does become O(1). They main benefit is signature aggregation not getting rid of the one or two op_codes. I think you're right in that it would need a hard fork tho.